volcano ice sea interaction in the cerro santa marta area northwest james ross island antarctic peninsula abstract we present here the results of detailed mapping lithofacies analysis and stratigraphy of the neogene james ross island volcanic group antarctic peninsula in the cerro santa marta area northwest of james ross island in order to give constraints on the evolution of a glaciated volcanic island our field results included recognition and interpretation of seventeen volcanic and glacial lithofacies together with their vertical and lateral arrangements supported by four new unspiked k ar ages this allowed us to conclude that the construction of the volcanic pile in this area took place during two main eruptive stages eruptive stages 1 and 2 separated from the cretaceous bedrock and from each other by two major glacial unconformities u1 and u2 the u1 unconformity is related to antarctic peninsula ice sheet expansion during the late miocene before 6 2 ma and deposition of glacial lithofacies in a glaciomarine setting following this glacial advance eruptive stage 1 6 2 4 6 ma volcanism started with subaerial extrusion of lava flows from an unrecognized vent north of the study area with eruptions later fed from vent s centered at cerro santa marta volcano where cinder cone deposits and a volcanic conduit lava lake are preserved these lava flows fed an extensive 7 km long hyaloclastite delta system that was probably emplaced in a shallow marine environment a second unconformity u2 was related to expansion of a local ice cap centered on james ross island which truncated all the eruptive units of eruptive stage 1 concomitant with glacier advance renewed volcanic activity eruptive stage 2 started after 4 6 ma and volcanic products were fed again by cerro santa marta vents we infer that glaciovolcanic eruptions occurred under a moderately thin 300 m glacier in good agreement with previous estimates of paleo ice thickness for the james ross island area during the pliocene

soft sediment deformation in the shallow submarine slope off nice france as a result of a variably charged pliocene aquifer and mass wasting processes abstract along the ligurian slope near nice southeastern france a combination of natural and man made factors govern slope stability and contributed to a devastating tsunamigenic landslide near nice airport in 1979 based on a total of 72 gravity and kullenberg cores we characterise the architecture and facies of the subbottom sediment a total of six sedimentary facies types were observed three of which represent the pliocene holocene background sediment in the wider nice area while another three are associated with the 1979 landslide and tsunami the three primary facies types are soft silty clay clayey silt somewhat indurated silt sand interbeds and pliocene conglomerates underlying the former the three other facies are poorly sorted mass wasting deposits up to pebble size silt representing the finer fraction of the mobilised mass and a tsunami related bed into which plant debris and artefacts got amalgamated accompanying geotechnical results attest that significant strength variations exist when comparing measurements from the narrow shelf shelf break and shallow slope as well as the 1979 slide scar factors such as groundwater charging in the more permeable horizons further lower the effective stress and in places approach lithostatic above such permeable silt sand beds deformation of soft clay is observed suggesting that leaching of ions from the clay mineral surfaces and frayed edges also facilitates weakening and creep micro slumping and folding elevated water supply as well as hydraulic fracturing of the clayey sediment is further attested by pipes of cm diameter and several decimeters length which entrained very soupy mud in the shallowmost deposits in and landward of the slide scar we also observe remnants from the catastrophic deposition associated with the 2 3 m high tsunami wave triggered in 1979 as attested by amalgamated sea grass and artefacts based on our observations and measurements on core scale and earlier models based on in situ cptu we suggest that a significant part of the quaternary delta and slope apron deposits are prone to being mobilised without a large external trigger so that all in all a high risk for a landslide event of considerable size off nice international airport is identified

gravity modelling of the litho asthenosphere system in the central mediterranean abstract the results of the 2 5 d gravity modelling of the litho asthenosphere system in the central mediterranean along two regional geotransects are presented and their possible implications for the geodynamical evolution of this area are discussed particularly gravity data on the tyrrhenian and provencal balearic basins were interpreted introducing significant constraints by means of several main petro physical parameters tied to the litho asthenospheric evolution during the extensive tectonics by this approach based on the model of mckenzie and bickle in j petrol 29 pp 625 679 1988 and white and mckenzie in j geophys res 94 b6 pp 7685 7729 1988 the estimation of the vertical density distribution in the lithosphere asthenosphere system has been possible significant differences in the gravity anomaly field occur when different density models of asthenospheric upwelling are considered this depends on factors like the thermal regime the stretching of the lithosphere and its thickness before it the obtained results contributed to the validation of models interpreting the origin of the tyrrhenian and ligurian provencal basins as related to a passive extensional process rather than to the presence of an active upwelling asthenosphere beneath the central mediterranean basins

evidence for orbitally controlled size variations of the east antarctic ice sheet during the late miocene ocean drilling program site 1165 penetrated drift sediments on the east antarctic continental rise and recovered sediments from a low energy depositional environment the sediments are characterized by prominent alternations between a green to greenish gray diatom bearing hemipelagic facies and gray to dark gray hemiturbiditic facies our investigation of an upper miocene section using high resolution color spectra multisensor core logs and x ray fluorescence scans reveals that sedimentation changes occur at milankovitch orbital frequencies of obliquity and precession we use this finding to derive an astronomical calibrated time scale and to calculate iron mass accumulation rates as a proxy for sediment accumulation rates terrigenous iron fluxes change by as much as 100 during each obliquity cycle this change and an episodic pattern of enhanced ice rafted debris deposition during times of deglaciation provide evidence for a dynamic and likely wet based late miocene east antarctic ice sheet eais that underwent large size variations at orbital time scales the dynamic behavior of the eais implies that a significant proportion of the variability seen in oxygen isotope records of the late miocene reflects antarctic ice volume changes

density changes in upwelling mantle abstract gravity modelling of the litho asthenosphere system in regions involved in extensional tectonics requires an accurate estimation of the vertical density profile in the upwelling asthenosphere to this end the calculation of the variation of several parameters is needed i e the degree of thermal anomaly in the asthenosphere the amount of stretching the thickness of the lithosphere before stretching and the variation of melt fraction generated by adiabatic decompression therefore knowledge of melt density and of the residual mantle rock composition is necessary in order to have the information to calculate the density of the uprising mantle these calculations allow to partially solve the problem related to ambiguity of the gravity interpretation and to provide information about the structural features of the upwelling mantle

deficiencies in the diatom evidence for a pliocene reduction of the east antarctic ice sheet evidence for pliocene reduction of the east antarctic ice sheet eais has been inferred from the presence of pliocene planktic marine diatoms in tills of the sirius group now exposed along the slopes of the transantarctic mountains we highlight deficiencies in this diatom evidence for a pliocene reduction of the eais first we examine what diatom habitats are left behind by a retreating ice sheet in this case the fennoscandian ice sheet fis and find that diatoms should occur in planktic and benthic marine brackish water freshwater and terrestrial habitats we expect that during former reexpansions these diverse diatom assemblages were picked up by the advancing fis and deposited in tills this is shown to be the case and diatoms found in tills from sweden and finland reflect the many habitats over which the fis passed if there was a reduction of the eais during the pliocene followed by renewed glaciation diatoms from many different habitats should be found in the resulting tills of the sirius group this is not the case only marine planktic diatoms and a few freshwater forms are reported similarly vertical downsection distribution of diatoms in sirius group and fennoscandian tills differ while in the sirius group diatoms appear restricted to surface and near surface sediments in fennoscandia they are found throughout the tills such data do not support a pliocene reduction model for the eais

temperature and density of the tyrrhenian lithosphere and slab and new interpretation of gravity field in the tyrrhenian basin abstract the gravity anomaly field of the tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the oligocene miocene they can resume in lithospheric thinning and asthenospheric rising beneath the tyrrhenian basin coexisting with the roll back subduction of the african plate margin westward sinking beneath the calabrian arc the geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects a model of the litho asthenospheric structure of this region is suggested showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro physical features of the mantle the first phase of this study consisted of the computation of the isotherms in the crust mantle system beneath the tyrrhenian basin and afterwards of the density distribution within the partially melted upwelling asthenosphere the second phase consisted of a temperature density modelling of the slab subducting beneath the calabrian arc finally a 21 2 interpretation of gravity data was carried out by including as constraints the results previously obtained thus the final result depicts a model matching both gravity thermal and petrographic data they provide a a better definition of the thermal regime of the passive mantle rise beneath the tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and b a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works

etude de l equilibre isostatique dans le sud ouest de l ocean indien a l aide des resultats de refraction sismique abstract the aseismic ridges of the southwestern indian ocean are in isostatic equilibrium with respect to the adjacent deep basins the structural units can be split into two different groups according to their mean crustal densities we demonstrate that the crustal thickness within the two groups is a linear function of the water depth this relationship expresses the airy isostatic equilibrium however the southern domain of the madagascar ridge is balanced neither with the northern domain of the ridge nor with any other unit of the area of study the northern domain has undergone only slight subsidence since the middle eocene while the southern domain would have rapidly subsided since the early miocene

crustal features along a w e tyrrhenian transect from sardinia to campania margins central mediterranean abstract the tyrrhenian sea is a neogene back arc basin formed by continental extension at the rear of the eastward migrating apennine subduction system its central part generated from tortonian to pliocene includes the sardinia rifted margin to the west an area with large volcanoes in the deep central sector and the campania rifted margin to the east a reprocessing of some 2000 km of mcs lines a new swath bathymetric map and a review of previous geological and geophysical data allow to analyse the nature and distribution of continental vs oceanic crust in this area which evolved in a short time span the central portion of the southern tyrrhenian sea is characterized by moho at about 10 km depth north of magnghi and vavilov smts this thinned crustal domain include a wide continent ocean transition with the occurrence of extensional allochthons and of serpenitinzed sub continental mantle recalling other well known rifted margins as the iberia one sectors floored by oceanic crust should occur mainly in the southern part of the study area but they do not appear related to discrete spreading ridges the continent ocean boundary cannot be drawn unequivocally in the area due also to the occurrence of widespread and huge magmatic manifestations not related to oceanic spreading these portions of the southern tyrrhenian sea represents therefore a complex oceanic back arc basin surrounded by magma rich rifted continental margins the abundant igneous manifestations and the very high stretching rates observed in the area may be related to the fact that the present tyrrhenian area was occupied by an orogenic domain affected by shortening until middle miocene times which is just before the late miocene onset of back arc extension the lithosphere in the region had then to be rheologically weak abundant generation and ascent of magmas mostly of ocean island basalt type was favoured by the large lithospheric permeability induced by strong extensional deformations

a revised pliocene record for marine 87sr 86sr used to date an interglacial event recorded in the cockburn island formation antarctic peninsula abstract we present a revised 87sr 86sr curve for marine sr in the interval 2 5 4 5 ma using analysis of orbulina universa from the middle pliocene type section in sicily punta piccola section and a mixed assemblage of planktonic foraminifera from odp site 758a and b the new calibration is used together with new 87sr 86sr analysis of pectenid calcite from cockburn island antarctica to confirm an age of 4 7 ma for the pectenids of the cockburn island formation formerly the pecten conglomerate a unit important in marking a period of warmth and possible glacial retreat in antarctica finally to aid interlaboratory comparison of 87sr 86sr data we calibrate a value of 0 709174 for en 1 against a value of nist 987 of 0 709248

impact of atmospheric co2 and galactic cosmic radiation on phanerozoic climate change and the marine δ18o record 1 a new model is developed and applied to simulate the phanerozoic evolution of seawater composition dissolved ca sr dissolved inorganic carbon alkalinity ph 18o marine carbonates sr ca 87sr 86sr 13c 18o atmospheric co2 and surface temperature the marine carbonate records sr ca 87sr 86sr 13c are used to reconstruct changes in volcanic tectonic activity and organic carbon burial over the phanerozoic seawater ph is calculated assuming saturation with respect to calcite and considering the changing concentration of dissolved ca documented by brine inclusion data the depth of calcite saturation is allowed to vary through time and the effects of changing temperature and pressure on the stability constants of the carbonate system are considered surface temperatures are calculated using the geocarb iii approach considering also the changing flux of galactic cosmic radiation gcr it is assumed that gcr cools the surface of the earth via enhanced cloud formation at low altitudes the 18o of marine carbonates is calculated considering the changing isotopic composition of seawater the prevailing surface temperatures and seawater ph repeated model runs showed that the trends observed in the marine 18o record can only be reproduced by the model if gcr is allowed to have a strong effect on surface temperature the climate evolution predicted by the model is consistent with the geological record warm periods cambrian devonian triassic cretaceous are characterized by low gcr levels cold periods during the late carboniferous to early permian and the late cenozoic are marked by high gcr fluxes and low pco2 values the major glaciations occurring during these periods are the result of carbon cycling processes causing a draw down of atmospheric co2 and a coevally prevailing dense cloud cover at low altitudes induced by strong gcr fluxes the two moderately cool periods during the ordovician silurian and jurassic early cretaceous are characterized by both high pco2 and gcr levels so that greenhouse warming compensated for the cooling effect of low altitude clouds the very high jurassic 18o values observed in the geological record are caused by low ph values in surface waters rather than cold surface conditions

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

seismic structure of the central tyrrhenian basin geophysical constraints on the nature of the main crustal domains in this work we investigate the crustal and tectonic structures of the central tyrrhenian back arc basin combining refraction and wide angle reflection seismic was gravity and multichannel seismic mcs reflection data acquired during the medoc mediterraneo occidental 2010 survey along a transect crossing the entire basin from sardinia to campania at 40 n the results presented include a 450 km long 2 d p wave velocity model obtained by the traveltime inversion of the was data a coincident density model and a mcs poststack time migrated profile we interpret three basement domains with different petrological affinity along the transect based on the comparison of velocity and velocity derived density models with existing compilations for continental crust oceanic crust and exhumed mantle the first domain includes the continental crust of sardinia and the conjugate campania margin in the sardinia margin extension has thinned the crust from 20 km under the coastline to 13 km 60 km seaward similarly the campania margin is also affected by strong extensional deformation the second domain under the cornaglia terrace and its conjugate campania terrace appears to be oceanic in nature however it shows differences with respect to the reference atlantic oceanic crust and agrees with that generated in back arc oceanic settings the velocities depth relationships and lack of moho reflections in seismic records of the third domain i e the magnaghi and vavilov basins support a basement fundamentally made of mantle rocks the large seamounts of the third domain e g vavilov are underlain by 10 20 km wide relatively low velocity anomalies interpreted as magmatic bodies locally intruding the mantle

a 550 km long moho traverse in the tyrrhenian sea from o b s recorded pn waves six obs deployed on a 550 km line in the tyrrhenian sea furnish reversed and overlapping profiles from 43 shots at 12 km intervals head waves recorded from a 8 km s refractor the moho permitted the computation of the crustal thickness which shows this basin to be underlain by an oceanic type of crust at least in two 100 km wide regions variations of pn arrival times mirror strong topographical changes of the moho differences in dips at the extremities towards corsica and calabria are documented

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

errata neogene fjordal sedimentation on the western margin of the lambert graben east antarctica the lambert graben is occupied by the world s largest fjord system through which flows the lambert glacier the amery ice shelf and their tributaries along the western margin of the graben in the northern prince charles mountains remnants of uplifted miocene and pliocene strata of the glacigenic fjordal pagodroma group total more than 800 m in thickness these sediments provide evidence for a dynamic east antarctic ice sheet during the neogene period each of the four pagodroma group formations defined from this region rests unconformably on either proterozoic or permo triassic rocks the unconformity surfaces represent parts of the walls and floors of neogene fjords for these surfaces to have been eroded the ice must have been grounded out as far as the continental shelf in prydz bay the pagodroma group was deposited by wet based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern antarctic ice masses the principal lithofacies are massive diamicts and soulder gravels deposited both close to a calving grounded glacier terminus and from icebergs the few stratified diamicts are the product of more distal iceberg sedimentation an ice transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts some lithofacies contain evidence of subaquatic slumping and gravity flowage volumetrically minor lithofacies include laminites with some exposures exhibiting large ice rafted clasts the laminites represent less proximal mainly ice free fjordal sediments resulting either from tidal current sorting of suspended sediment originating from subaquatic glaciofluvial discharge or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment the pagodroma group provides a record of multiple glaciation by dynamic sliding glaciers carrying large amounts of both basal and supraglacial debris the closest modern analogues in terms of the thermal and dynamic characteristics of the neogene lambert glacier appear to be the fast flowing tidewater glaciers of east greenland these glaciers originate from the interior ice sheet and discharge large volumes of icebergs the resulting lithofacies are predominantly diamicts

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

mid pliocene to recent abyssal current flow along the antarctic peninsula results from odp leg 178 site 1101 abstract sediments recovered from a drift deposit located on the pacific side of the antarctic peninsula odp leg 178 site 1101 give a physical record of a bottom current sourced from the weddell sea deep water for the past 3 ma sediment grain size and magnetic fabric analyses indicate a contourite depositional environment and little change in the average intensity of this current terrigenous fluxes decreased around the time of the onset of northern hemisphere glaciation which we interpret as a freezing of the base of the antarctic peninsula ice cap terrigenous fluxes have increased since 1 7 ma implying a possible return of the antarctic peninsula ice cap to a more wet based ice sheet

new data and hypothesis on the development of the tyrrhenian basin abstract among those basins which developed during the neogene and quaternary at the rear of the perimenditerranean mountain chains the tyrrhenian basin is the most recently formed comparing the available geological and geophysical data the tyrrhenian domain and its neighbourhoods can be divided into more or less homogeneous sectors namely northern and southern tyrrhenian apenninic chain maghrebides chain apulian and iblean african foreland ionian foreland for each sector the different phenomena involved and the crustal characteristics are discussed the evolution of the domain has been explained by the application of a crustal stretching model developed for continental margins this approach predicts the formation of basinal areas as a result of the europe africa collisional movements within a plastic rigid deformation model taking into account the mass redistribution after collision the model explains both the distension developed within the collisional system and the penecontemporaneous development of compressive and distensive phases as a consequence of the intraplate stresses horizontal shearings affecting the whole lithosphere at different levels occur with delaminations asthenosphere uprising and gradual collapse in the upper crust e w trending and strike slip dextral faults played a primary role in the evolution of the tyrrhenian basin inducing the largest tearings at the end of the major transcurrent systems such an evolution is complicated by the migrating motion of the shear zone from n to s and by the penecontemporaneous stop in the extension from the northern towards the southern domains of outstanding importance is the shear zone which borders the southern tyrrhenian enabling the opening of the basin and allowing the development of the major group of en echelon sub basins with a nw se trend

linkages between east antarctic ice sheet extent and southern ocean temperatures based on a pliocene high resolution record of ice rafted debris off prydz bay east antarctica 1 ice rafted debris mass accumulation rates ird mar at a drill site on the antarctic continental margin are investigated to evaluate the linkages between east antarctic ice sheet extent and southern ocean temperatures in the early to mid pliocene odp site 1165 is within 400 km of the antarctic coastline and in the direct pathway of icebergs released by the amery ice shelf the amery ice shelf is the largest ice shelf in east antarctica and it buttresses the lambert glacier drainage system which accounts for 14 of the outflow from the east antarctic ice sheet ird mar were low during peak southern ocean warming in the early pliocene after a brief precursor a tenfold increase in ird mar at 3 3 ma marks the termination of the early pliocene ice sheet minimum coincident with the m2 glacial for the mid pliocene a strong correlation exists between the high amplitude signal in the lr04 benthic stack and ird mar suggesting linkages between east antarctic ice extent global ice volume and deep water temperatures the ird record at site 1165 provides evidence of greater sensitivity of the lambert glacier amery ice shelf system to southern ocean warming than is currently predicted by ice sheet models which may relate to uncertainties in the understanding of ocean heat uptake poleward heat transport and ice sheet ocean interactions

variations of stress directions in the western alpine arc summary the western alpine arc originated during the cretaceous orogenesis as a consequence of the continental collision between the european and adriatic plates the distribution of forces acting in this sector of the alps is still somewhat uncertain in the past some evorts have been made to map the distribution of p and t axes but it is known that these can be substantially diverent from the principal stress directions in recent work we presented a first attempt to determine the directions of s 1 and s 3 which we could compute only for a local regime at the level of the magnitude of the larger events that occurred in the area to obtain the stress orientation we applied the technique developed by gephart and forsyth to invert fault plane solutions in this work we present the results of a detailed analysis performed on a larger area applying the same methodology a total of 86 earthquakes with magnitudes ranging from 2 5 to 5 3 has been used for inversion the results confirm the impossibility of defining within the available data a regional stress field in fact diverent local behaviours have been demonstrated in four subregions for the first subregion namely the northern part of the western alps the inversion of 28 earthquakes resulting in a misfit of 5 9 revealed a distensive regime orientated n s for the second subregion the outer part of the western alps the inversion of 16 earthquakes led to a misfit of 5 3 for a distensive e w orientated regime in the inner part of the chain an opposite result was obtained by the inversion of 14 earthquakes confirmed by a misfit of 4 7 finally the region of the ligurian sea revealed an almost horizontal nw se orientated s 1 whereas s 3 is ne sw orientated with a dip of around 30 40 the inversion for this subarea was carried out on a data set of 28 earthquakes and characterized by a misfit of 7 1 the uncertainty of the stress axis orientation 90 per cent confidence limits is on average for all inversions around 40

pliocene pleistocene diatoms in paleozoic and mesozoic sedimentary and igneous rocks from antarctica a sirius problem solved there are two competing scenarios on the behavior of the east antarctic ice sheet during the late tertiary in one scenario the ice sheet was very dynamic and underwent major drawdown and renewal as late as the pliocene in the other the ice sheet was relatively stable during the late neogene the presence of marine diatoms in sirius group sedimentary rocks in east antarctica is at the center of the disagreement one side regards the diatoms as the major piece of evidence to support the drawdown and renewal hypothesis and infers that they were introduced into the sirius during renewed glaciation of east antarctica others suggest that these diatoms were likely introduced into the sirius by atmospheric largely eolian processes we propose a simple test of the eolian hypothesis if diatoms were introduced into the sirius by eolian processes then they should also be present in older paleozoic and mesozoic sedimentary and igneous rocks samples from two units of the beacon supergroup devonian to jurassic from beacon valley east antarctica were analyzed the beacon heights orthoquartzite devonian and the feather conglomerate permian triassic also examined was sediment found in cracks of paleozoic and mesozoic devonian to cretaceous igneous rocks from marie byrd land west antarctica largely pliocene pleistocene planktonic marine diatoms were found in all sample sets because neither beacon supergroup sedimentary rocks nor igneous rocks from marie byrd land are pliocene pleistocene in age such findings strongly suggest that diatoms were introduced into them by eolian processes this same scenario can be applied to sirius group sedimentary rocks

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

a seismic refraction experiment in the tyrrhenian sea summary we present the results of two 100 km long reversed seismic refraction lines shot in the tyrrhenian sea using explosive sources and oceanbottom receivers the results have been interpreted using ray tracing through laterally varying structures the more easterly line t2 was shot in the central part of the tyrrhenian abyssal plain in a water depth of 3 5 km the crust here is shown to be oceanic in character but to exhibit significant lateral heterogeneity the upper part of the crust layer 2 contains a steep velocity gradient from about 4 to over 6 km s l at a depth of typically 2 km the lower part of the crust layer 3 contains a smaller velocity gradient from 6 6 to 6 9 km s l at the base of the crust total crustal thickness is between 6 and 8 km the other line t1 carried out in the cornaglia basin in 2 7 km of water reveals a more complicated velocity structure we conclude that its southern half is underlain by oceanic crust similar to that observed at t2 however its northern half appears to be underlain by crust of similar thickness but in which seismic velocities increase slowly with depth from 4 9 km s l immediately below the superficial sediments to 6 3 km s l at the moho we interpret this latter structure as thinned continental crust surprisingly neither the seafloor topography nor the depth to moho reflect the transition from oceanic to continental crust we infer from these results that although the southern and eastern parts of the tyrrhenian basin were formed primarily by seafloor spreading much of the basin north of about 40 n and probably including some areas with water depths in excess of 3 km is underlain by thinned continental crust the evolution of the northern part of the tyrrhenian basin must therefore have occurred chiefly through a process of continental extension which in some areas has reduced crustal thickness to as little as 6 8 km south of 40 n

mesozoic climate liverworts and all the relationship between carbon dioxide and climate over millions of years has been a source of controversy fossilized liverwort leaves can help illuminate both temperature and atmospheric carbon dioxide levels from 200 to 60 million years ago

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

pleistocene collapse of the west antarctic ice sheet some glacial sediment samples recovered from beneath the west antarctic ice sheet at ice stream b contain quaternary diatoms and up to 108 atoms of beryllium 10 per gram other samples contain no quaternary diatoms and only background levels of beryllium 10 less than 10 6 atoms per gram the occurrence of young diatoms and high concentrations of beryllium 10 beneath grounded ice indicates that the ross embayment was an open marine environment after a late pleistocene collapse of the marine ice sheet

co2 forced climate thresholds during the phanerozoic abstract the correspondence between atmospheric co2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity here i compare 490 published proxy records of co2 spanning the ordovician to neogene with records of global cool events to evaluate the strength of co2 temperature coupling over the phanerozoic last 542 my for periods with sufficient co2 coverage all cool events are associated with co2 levels below 1000 ppm a co2 threshold of below 500 ppm is suggested for the initiation of widespread continental glaciations although this threshold was likely higher during the paleozoic due to a lower solar luminosity at that time also based on data from the jurassic and cretaceous a co2 threshold of below 1000 ppm is proposed for the initiation of cool non glacial conditions a pervasive tight correlation between co2 and temperature is found both at coarse 10 my timescales and fine resolutions up to the temporal limits of the data set million year timescales indicating that co2 operating in combination with many other factors such as solar luminosity and paleogeography has imparted strong control over global temperatures for much of the phanerozoic

controls on the global distribution of contourite drifts insights from an eddy resolving ocean model abstract contourite drifts are anomalously high sediment accumulations that form due to reworking by bottom currents due to the lack of a comprehensive contourite database the link between vigorous bottom water activity and drift occurrence has yet to be demonstrated on a global scale using an eddy resolving ocean model and a new georeferenced database of 267 contourites we show that the global distribution of modern contourite drifts strongly depends on the configuration of the world s most powerful bottom currents many of which are associated with global meridional overturning circulation bathymetric obstacles frequently modify flow direction and intensity imposing additional finer scale control on drift occurrence mean bottom current speed over contourite covered areas is only slightly higher 2 2 cm s than the rest of the global ocean 1 1 cm s falling below proposed thresholds deemed necessary to re suspend and redistribute sediments 10 15 cm s however currents fluctuate more frequently and intensely over areas with drifts highlighting the role of intermittent high energy bottom current events in sediment erosion transport and subsequent drift accumulation we identify eddies as a major driver of these bottom current fluctuations and we find that simulated bottom eddy kinetic energy is over three times higher in contourite covered areas in comparison to the rest of the ocean our work supports previous hypotheses which suggest that contourite deposition predominantly occurs due to repeated acute events as opposed to continuous reworking under average intensity background flow conditions this suggests that the contourite record should be interpreted in terms of a bottom current s susceptibility to experiencing periodic high speed current events our results also highlight the potential role of upper ocean dynamics in contourite sedimentation through its direct influence on deep eddy circulation

the opening processes in the deep tyrrhenian basins of marsili and vavilov as deduced from magnetic and chronological evidence of their igneous crust abstract shapes and chronology of magnetic anomalies of the mafic crust flooring the marsili and vavilov abyssal plains in the central tyrrhenian sea are discussed in the marsili deep basin the possible 3 phase evolution of a magmatic tectonic process of spreading is considered the early magmatic phase apparently took place at the time of the olduvai magnetic event 1 87 to 1 67 ma b p site 650 of the ocean drilling project leg 107 it appears to consist of spreading manifestations of a low magnetic intensity and a round shape forming the igneous basement around the marsili volcano the late phase was characterized by a spreading process exhibiting a linear configuration and high intensity of the magnetic anomalies organized spreading this phase of the brunhes epoch has given rise to the great marsili volcano emplaced in the basin s central part the intermediate phase shows reversed magnetic polarity and slightly elongated shapes it appears to have developed in late matuyama times from 1 67 to 0 73 ma ago the intensities of the magnetic anomalies in the basin of vavilov are on the whole lower than those present in the magnetic field of the marsili also in the vavilov deep basin the magnetic anomalies associated with the early volcanic manifestations which are of late miocene age about 7 5 ma are characterized by low intensity and a round shape whereas those associated with the effusions on the vavilov volcano whose age ranges from late pliocene to late quaternary from 2 4 to less than 0 12 ma exhibit a high intensity and a linear shape the two bathyal plains have inter arc structural settings from west to east the vavilov bathyal plain is bordered by the orogenic volcanic belt of the island of sardinia and maybe a central tyrrhenian arc the latter and the arc of the eolie which is active in the present time border the marsili plain the ages of the early spreading processes in the bathyal plains respectively from about 10 to 6 ma and from 1 9 to 1 3 ma appear to represent distinctive temporal markers in fact they may be coincident with the periods of quiescence of the volcanic activity that affected the adjoining arcs

seismicity and crustal structure beneath the western ligurian sea derived from local earthquake tomography abstract in this paper we present and comment on the results of a tomographic inversion of p arrival times of local earthquakes to better understand the structure and features of the ligurian sea an oceanic basin originated in the oligocene miocene this tomographic inversion is the last step in a long and careful revision of the data available for the ligurian sea an accurate catalogue derived from a controlled compilation of data from the numerous stations monitoring seismic activity in this young oceanic basin has been used for computation of a one dimensional 1d reference model a high quality subset of the new catalogue has been used for the non linear 3d tomographic inversion by iteratively solving the coupled hypocenter velocity problem in a least square sense careful analysis of the resolution capability of the used data set has revealed the better resolved features for interpretation the resulting 3d model shows a high velocity layer extending from the northeastern side of the model where it lays about 30 km deep to the southwestern part where it shallows to 15 km the shallow part of this high velocity body is located near the original area of the opening of the ligurian sea that took place between the oligocene and early miocene its velocity is comparable with that of an oceanic moho around 7 8 km s a lens shaped high velocity body about 25 km long located at a depth of 8 15 km is interpreted as a series of ophiolitic bodies intruded into the upper crust

structural evolution of the tyrrhenian back arc basin abstract the tyrrhenian basin has developed as a marginal basin through drifting of the calabrian sicilian arc system towards the east southeast the main structural features of the basin result from this movement the tensional structures normal faults of the margins are mainly aligned n10 to n30 e the transform faults are oriented n110 n120 e except for a previous structuralization linked to the western mediterranean rifting and drifting the first extensional movements affected the tyrrhenian area as early as lower miocene time during the post burdigalian nevertheless the main rifting phase which led to oceanic accretion was initiated during the late tortonian the narrow central oceanic area generated mainly around the early pliocene is restricted to the rift s axis the marginal basin type of evolution of the tyrrhenian sea is most probably directly linked to subduction of the ionian lithosphere nevertheless interferences between collision in the surrounding apennines calabria or sicilides and subduction processes have dominated this special back arc basin evolution since late tortonian time the tyrrhenian arc shows a regional n120 e oriented tensional pattern short compressional events occur briefly in middle pliocene and middle pleistocene times correlated with brief paroxysmal phases of extension and subsidence the deformation depends on the presence of a subduction zone parallel to the calabrian arc swell which allows the migration of the unblocked segments of the arc in a n120 e direction

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

thermal evolution of a rift basin the tyrrhenian sea existing geological and geophysical data support the view that the opening of the tyrrhenian sea was by rifting of a formerly continuous continental lithosphere which began in upper miocene on the upper sardinian margin and migrated southeastward to the calabria margin heat flow across the tyrrhenian sea shows a pronounced asymmetry from about 50 70 mw m 2 over the sardinian margin to more than 150 mw m 2 over its southeastern margin off southern italy and calabria in this study we use the newly acquired data from ocean drilling program leg 107 heat flow seismic velocity and bathymetric data to constrain a group of models that supposes the tyrrhenian sea opened by detachment of a formerly continuous lithosphere along a southeastern facing low angle normal fault specific models tested include 1 the wernicke model in which thinning and extension of the continental lithosphere are supposed to be accomplished by simple shear along a large scale gently dipping detachment fault zone which cut through the entire lithosphere and 2 the delamination model in which the low angle detachment fault is supposed to cut only the upper and middle crust but to merge subhorizontally into the lower crust below which concurrent pure shear may occur a versatile two dimensional finite element procedure is used to evaluate the tectonic and thermal evolution of these models and the results are compared with observations to test the validity of the models delamination models with large pure shear components in the lower lithosphere and the wernicke model predict heat flow within 1 of the measurements the wernicke model however predicts a basin configuration much too deep in comparison with bathymetry and a subbasinal lithospheric thickness substantially different from rayleigh wave dispersion results the delamination model with a large component of pure shear in the subbasinal lower lithosphere on the other hand predicts satisfactorily both the bathymetry and the lithospheric thickness beneath the basin

use of grain size and magnetic fabric analyses to distinguish among depositional environments the combined use of grain size and magnetic fabric analyses provides the ability to discriminate among depositional environments in deep sea terrigenous sediments we analyzed samples from three different depositional settings turbidites pelagic or hemipelagic interlayers and sediment drifts results indicate that sediment samples from these different environments can be distinguished from each other on the basis of their median grain size sorting as well as the intensity and shape of magnetic fabric as determined from an examination of the anisotropy of magnetic susceptibility we use these discriminators to interpret downcore samples from the bermuda rise sediment drift we find that the finer grains of the bermuda rise relative to the blake outer ridge do not result from lower depositional energy current speed and so may reflect a difference in the nature of sediment being delivered to the site i e distance from source between the two locations

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

regional seismic phases across the ligurian sea lg blockage and oceanic propagation abstract the ligurian sea west mediterranean is an example of a narrow oceanic basin which stops lg wave propagation locating the exact point of lg extinction was one of the goals of the sisbalig ii seismological experiment which deployed both inland stations in provence and corsica and ocean bottom seismometers obs in the ligurian sea a precise analysis of all available regional seismological data using energy diagrams reveals the role of the provence margin in the lg phase extinction for seismic events occurring in the southwestern alps the extinction is not a progressive phenomenon along oceanic travel path but occurs in a narrow zone of about 20 km width in the vicinity of the provence margin the extinction is accompanied by the generation of two types of diffracted waves the mantle phase sn v s 3 5 km s 1 and very low velocity s waves appearing both near the provence margin and in the middle of the ligurian basin we performed numerical simulation of sh wave propagation in two dimensional 2d media to investigate the mechanisms of lg extinction the simulations confirm that simple crustal thinning at the continent ocean boundary alone cannot cause the observed extinction of lg waves although the change in moho depth does induce the diffraction of a part of the incident lg wavetrain into mantle waves giving rise to the sn phase on the other side of the basin the existence of soft oceanic sediments is a very important factor in explaining the extinction as a large part of the lg energy is transferred into slow s waves trapped in the sediments moreover comparison of synthetic seismograms and observed data shows that the observed two packets of low velocity waves are an indication of the asymmetry of the ligurian basin with the existence of two shallow basins with very low s velocity 1 0 km s 1 near the provence margin and in the middle of the ligurian sea however the attenuation of lg waves in the vicinity of the provence margin is more abrupt in the data than in the simulations this discrepancy could result from the complex geometry of the continent ocean transition zone and its possibly very diffractive nature two factors that could add to lg extinction at the margin and are impossible to take into account in models

antarctic environmental variability since the late miocene odp site 745 the east kerguelen sediment drift abstract characterization of sediment from ocean drilling program site 745 representing the east kerguelen ridge sediment drift addresses important issues surrounding the timing of miocene to present east antarctic ice sheet stability and oceanic environmental change our results show three periods of greatly enhanced accumulation of antarctic derived sediment at 6 4 5 9 ma 4 9 4 4 ma and 1 1 0 8 ma potentially indicative of warmer less stable ice sheets at these times conversely the accumulation of antarctic derived material is comparatively less during the middle of the pliocene warm epoch 4 8 3 2 ma the deep flow forming the kerguelen drift was stronger during the latest miocene and earliest pliocene and has decreased in intensity continuously since then

earthquake relocation in the ligurian sea western mediterranean geological interpretation abstract relocated epicenters are computed with a model based on complex local structure i e oceanic floor in the central ligurian basin and thinned continental margins by superposing these relocated earthquakes on a basement bathymetric map the structural relations are clearly demonstrated compressive stress towards the west northwest is confirmed in the northern ligurian basin by focal mechanism study according to our results most of the earthquakes appear to be shallow and linked to rejuvenation of older distensive and strike slip structures on margins as in the basin by a compressional motion

miocene rotation of sardinia new paleomagnetic and geochronological constraints and geodynamic implications the miocene rotation of sardinia western mediterranean remains poorly constrained despite a wealth of paleomagnetic data primarily due to poor chronostratigraphic control however this rotation is contemporaneous with the opening of the liguro provencal back arc oceanic basin and its history is key to understanding the kinematics of opening of the western mediterranean we address this issue through paleomagnetic and 40ar 39ar geochronological investigations of miocene volcanic sequences in sardinia precise age control allows secular variation of the geomagnetic field to be evaluated these data provide constraints on the rotational history of this continental microplate sardinia rotated 45 counterclockwise with respect to stable europe after 20 5 ma aquitanian which is a marked increase over the estimate of 30 derived from prior paleomagnetic studies rotation was essentially complete by 15 ma about 30 of rotation occurred between 20 5 and 18 ma burdigalian corresponding to the period of maximum volcanic activity in sardinia the observed rotation validates palinspastic models derived from a morphological fit of basin margins and indicates high rates of opening up to 9 cm yr 1 in the southern part of the basin between 20 5 and 18 ma

structural constraints on the tertiary plate tectonic evolution of italy abstract eight cross sections six of which were balanced and restored using the principles of thin skinned tectonics demonstrate the reinterpretation of the apennine and sicilian mountains as a detached fold and thrust belt the thin skinned interpretation constrains the extent of the restored continental margins and the amount percentage direction and timing of tectonic shortening allowing the development of a plate tectonic model late cretaceous and paleogene subduction to the north beneath the corsica sardinia calabria csc microplate causes rifting from se france and the development of oceanic crust between the two in the oligo miocene the late oligocene collision of adria and northernmost csc pins the northern edge of the csc plate causing its counter clockwise rotation and its mid miocene suturing between italy and sicily the n s convergence of africa and europe with counter clockwise rotation of italy causes shortening in the nne ssw direction in italy and sicily from 20 10 ma the n s compression extrudes calabria to the se causing mio pliocene compression in southern italy and eastern sicily at the same time as extension and alkaline volcanism in central italy

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

a closing ligurian sea two earthquakes occurred in the ligurian sea in december 1989 and april 1990 both were widely felt along the french and italian rivieras thus reminding us of the seismic risk in this region the significant increase in the number of seismic stations in the area facilitated the study of these two shocks and their related aftershocks using different techniques absolute and relative hypocentral locations doublet analysis and waveform modeling we computed accurate hypocentral locations and estimated the location error range for earthquakes in this area we also computed the focal mechanisms for both mainshocks and we present here a synthesis that integrates previous data the reactivation in compression of the ligurian sea sphenochasm is confirmed which would eventually result in the closing of an aborted oceanic domain as the seismic activity is clearly restricted to the northern margin we suggest it locally results from the lateral expulsion of the south western alps along the apulian indenter

neogene evolution of the southwestern tyrrhenian sea sardinia basin and western bathyal plain abstract the reprocessing of mcs reflection lines and sampling data across the sw tyrrhenian basin from the sardinia tunisia strait sts to the orosei canyon line ocl show that the acoustic basement of the area is made by variscan crystalline metamorphic rocks covered by a thick sequence of sediments including the messinian interval the pre messinian sequence can be subdivided into three seismic intervals or subunits largely calibrated by sampling data the oldest pre messinian subunit is strongly deformed by compressional and or transpressional structures and the recovered samples are deep water arkosic sediments aquitanian in age however the whole interval may encompass a wider time span probably from late oligocene to langhian this subunit was laid down in a fore arc basin located between a volcanic arc sardinia and an accretionary wedge calabrian peloritanian kabilide or ck units prior to the collision of the latter elements with the continental margin of africa in sicily and tunisia along the so called drepano thrust front dtf coeval to collision the generation of the main sardinia thrust mst occurred carrying the sardinia basement rocks over the ck units and deforming the fore arc basin sediments the intermediate pre messinian sedimentary subunit spans from part of serravallian to part of tortonian it is post tectonic with respect to the underlying subunit but it represents a pre rift succession if related to the overlying one it consists of terrigenous deposits prograding from sardinia to the ene into a basin some hundreds of meters deep which was left in the area after collision the youngest pre evaporitic subunit late tortonian early messinian in age displays wedge shaped reflectors in the sardinia basin and forms the lower portion of a syn rift complex including the messinian and part of the pliocene sediments this succession records the onset of extensional tectonics in the area as also testified by the tortonian age of exumation of the basement while in the tyrrhenian basin north of the ocl intra tortonian to intra pliocene rifting was strong but discontinuous and migrating with time to the east in the sw tyrrhenian basin in contrast rifting was less severe but continuous during the same time interval this emphasizes the role played by the ocl a inherited mesozoic discontinuity reactivated as a transfer zone during the neogene these new data allow correlation of the main miocene deformational events observed in the study area to those of the adjacent emerged areas namely the peloritani and maghrebian units in sicily prior to the pliocene quaternary full development of the southern tyrrhenian sea

the neogene east antarctic ice sheet a dynamic or stable feature abstract this paper is a review of the history and behaviour of the east antarctic ice sheet during the late neogene and is a response to the publication of sugden et al 1993a the case for a stable east antarctic ice sheet in geografiska annaler 75a 4 the antarctic ice sheet is a critical factor in the global climate and oceanographic system knowledge of its historical development is critical to understanding global palaeoceanographic and palaeoclimatic systems and their development the webb harwood hypothesis proposes that the ice sheet while being present in antarctica for more than 40 ma was until recently ca 2 5 ma a dynamic feature waxing and waning under a more temperate climatic and glaciologic regime the stabilistic hypothesis proposes that the current ice sheet has existed in its present cold and polar form for at least the last 14 ma the case for a stable east antarctic ice sheet is the clearest statement of the stabilistic argument to date the authors find support for their viewpoint by presenting evidence from several geologic data bases that does not support their own null meltdown hypothesisr which they deem to be equivalent to the webb harwood hypothesis thereby they conclude supporting the stabilistic hypothesis however their conclusions are weakened by failure to reject their null hypothesis conflict between the meltdown and webb harwood hypotheses infraction of geological laws and poor application of stratigraphic principles several issues are highlighted here as important for direction of future research and discussion concerning late cenozoic antarctic glacio climatic history

late miocene to pleistocene paleoceanographic records from the feni and gardar drifts pliocene reduction in abyssal flow magnetic fabric analyses from two north atlantic drift deposits provide proxies for determining relative variations in the strength of abyssal flow over the last 10 my the data show a cessation of current controlled sedimentation at the shallower feni drift 2417 m at the time of onset of northern hemisphere glaciation 2 6 ma drift formation ended nearly 2 my earlier 4 2 ma at the deeper gardar drift 3220 m implying stepwise reduction in deep water flow relatively light d 18 o values at the deeper gardar drift indicate a warmer thus also more salty water mass site prior to 6 ma we interpret this as representing mediterranean sea water which flowed north at depths greater than that of the feni drift site the supply of mediterranean water to the north atlantic was shut off as the gibraltar straits closed causing the messinian salinity crisis and never returned to that position in the water column after the mediterranean opened again d 2005 elsevier b v all rights reserved

neogene fjordal sedimentation on the western margin of the lambert graben east antarctica neogene glacial sedimentation east antarctica

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

did the antarctic ice sheets expand during the early pliocene seismic data show that glacial unconformities are located within lower pliocene strata on the antarctic continental shelves the glacial unconformities are significant because they provide direct evidence that the antarctic ice sheets advanced despite the generally warmer climates and elevated sea levels that characterized most of the early pliocene the magnitudes of peak eustatic lowstands and 18 o enrichments indicate that the ice volume on antarctica may have exceeded today9s ice volume by approximately 18 which suggests that the ice sheet grounding events on the shelves probably were associated with larger than present ice volumes on two to three occasions during the early pliocene

rotation of the italian peninsula from aeromagnetic evidence abstract palaeomagnetic data have been used extensively in order to study the geodynamical history of a region similar information can be obtained by analysing the shape of aeromagnetic anomalies and the direction of the total magnetization vector of the anomaly sources we can suppose that the direction of the earth s magnetic induction vector is almost constant with time along a n s direction if a significant directional difference between total magnetization and induction vector is observed we can argue that the anomaly sources were affected by conspicuous rotational movements in the central southern tyrrhenian area the anomaly shape is generally normal i e n s except for several anomalies which have a maximum minimum direction parallel to the italian coast that is nw se rather than n s this feature and the location of these anomalies on the border of the bathyal plain seems to be in agreement with the anticlockwise rotation movements suggested in some geodynamical models of the region

ionian basin and calabria arc some new elements from dss data abstract the interpretation of results from a 250 km long seismic refraction traverse recorded using ocean bottom seismometers in the northwestern ionian sea and a fan profile recorded across southern calabria have augmented previous studies by placing additional constraints on the tyrrhenian sea calabria ionian sea transition overlapping branches of pn phases confirm the existence of a thinned crust about 13 km giving rise to the major bouguer anomaly high of the central ionian basin a low average crustal velocity is observed throughout the basin in accordance with the very thick sedimentary cover exemplified by previous seismic surveys a deepening moho may be followed continuously from the centre of the basin to 40 km offshore from calabria where a sudden depth decrease 30 to 20 km is accompanied by a sharp change in the crustal velocity structure the estimated depth of such a shallower moho towards the northwest confirmed by a shot recorded in a fan geometry across southern calabria is in accordance with that found earlier for the southernmost margin of the tyrrhenian basin

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

amincissement de la croute et accretion au centre du bassin tyrrhenien d apres la sismique refraction seismic refraction lines were carried out in the deep central area of the tyrrhenian basin and near the foot of adjacent margins using air guns as seismic source and pop up bottom seismographs pubs valuable correlations between refraction and reflection data enable us to identify messinian and pre messinian series beneath plio quaternary series on stretched margins toward the middle of the basin detritic to volcanodetritic series overlay the acoustic basement the p wave velocity depth distributions inferred from synthetic seismograms on most of the profiles are similar to those computed for oceanic areas especially for spreading zones such as the atlantic ridge the east indian ridge the reykjanes ridge progressive velocity increasing with depth velocity inversions within the crust moho depth of 10 11 km low pn velocity of 7 73 km s 1 suggesting the existence of an abnormal mantle layer 3 is 7 km deep probably including a 2 km thick layer 3b 7 44 km s 1 our data are in good agreement with the assumption of a recent accretion beneath the central basin of the tyrrhenian sea along a cross section at 40 n latitude running from the sardinian to the apenninic margins the moho discontinuity rapidly rises from 27 km to 11 km depth beneath the central tyrrhenian basin the 6 0 km s 1 granitic layer beneath sardinia disappears east of the central fault and reappears again along the facing apenninic margin

inclusion of the weathering of volcanic rocks in the geocarbsulf model the carbon cycle model geocarbsulf is extended by dividing the weathering of silicates into volcanic and non volcanic rocks the proportion of volcanic weathering is calculated as a function of time from the oceanic record of 87sr 86sr the volcanic proportion is then used to modify the equations for calculating atmospheric co2 by the addition of a new non dimensional volcanic weathering factor the effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales and not sr isotopic data that had been used previously results indicate moderate change from geocarbsulf in the distribution of atmospheric co2 over phanerozoic time this includes an increased minimum in co2 during the late ordovician in agreement with the presence of a continental glaciation at that time and a shift of maximum mesozoic values from the jurassic to the early cretaceous

modeling pliocene warmth modeling studies relevant to the question of pliocene warmth are reviewed although significant regional climate variations may be due to pliocene changes in orography and ocean circulation these changes do not appear sufficient to explain inferred globally increased warmth climate modeling studies for a doubling of co2 suggest high latitude temperature increases approximately comparable to inferred warming during the pliocene i suggest that such a co2 increase may be primarily responsible for the pliocene temperature increase downdraw of co2 since the pliocene is consistent with some geochemical indications of enhanced weathering in the pleistocene however additional proxy testing of this hypothesis is required the co2 models also predict tropical sea surface warming of 2 3 c and winter temperature warming in central eurasia 50 70 n of 4 10 c predictions that distinguish co2 from some other mechanisms enhanced scrutiny of pliocene records from the above regions may prove a valuable test of the co2 hypothesis finally although a co2 increase may be responsible for pliocene warmth this time interval should not be cited as a direct analog for a future greenhouse warming as the future climate will have a significant nonequilibrium response because of the rapid rate of change of forcing despite these limitations enhanced study of pliocene climates may be very valuable as an independent source of validation of co2 doubling simulations

several location methods for underwater shots in the gulf of genoa western mediterranean structural implications abstract during the egt survey 50 underwater shots were detonated on a n s section through the gulf of genoa running from the northern margin 44 12 n towards corsica 42 90 n along the 9 e meridian the aim of this work is in a first stage to establish the propagation model of regional phases in this region and consequently to improve the location of epicentres and afterwards to refine our structural knowledge of this complex crustal area the relocation of these shots was carried out with arrival times of seismic signals recorded at land stations we have used different location methods all of which led to similar crustal models they reveal a low p n velocity area in the northern ligurian sea and in the gulf of genoa with a 20 km thick crust in the southern part approximately south of latitude 43 7n a 4 km thick oceanic crust covered by 8 km of sediments is clearly confirmed using these models a significant improvement of epicentre locations was obtained these improvements to propagation models lead to the two main structural conclusions 1 1 in the southern part of the investigated area the spread of an oceanic type domain as far as the foot of the continental margin 2 2 a sharp transition between the two domains of different stretching rate the northern one with a moho depth of about 20 km and the southern one with an average moho depth of about 14 km these observations substantiate the presence of a transform margin between the rifted gulf of genoa and the oceanic type ligurian basin

atmospheric carbon dioxide linked with mesozoic and early cenozoic climate change carbon isotopes of fossil plants and model simulations suggest that atmospheric carbon dioxide levels were variable during the period 200 to 60 million years ago the large decreases in the partial pressure of co2 coincide with glaciations providing evidence against climate co2 decoupling during the mesozoic

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

a physical record of the antarctic circumpolar current late miocene to recent slowing of abyssal circulation abstract sediments recovered from a drift deposit lying along the pacific margin of the antarctic peninsula odp leg 178 site 1095 provide a physical record of the antarctic circumpolar current since late miocene time determination of the strength of the magnetic fabric anisotropy of magnetic susceptibility provides a proxy for current strength fabric strength declines throughout the record from high values in the late miocene a pronounced step occurs between 5 0 and 5 5 ma and values decrease more gradually since about 3 0 ma the mass accumulation rate of terrigenous sediment derived from the antarctic peninsula indicates stabilization of the antarctic peninsula ice cap prior to about 8 5 ma

earthquake relocation using a 3d a priori geological velocity model from the western alps to corsica implication for seismic hazard the region between the inner zones of the alps and corsica juxtaposes an overthickened crust to an oceanic domain which makes difficult to ascertain the focal depth of seismic events using routine location codes and average 1d velocity models the aim of this article is to show that even with a rather lose monitoring network accurate routine locations can be achieved by using realistic 3d modelling and advanced location techniques previous earthquake tomography studies cover the whole region with spatial resolutions of several tens of kilometres on land but they fail to resolve the marine domain due to the absence of station coverage and sparse seismicity to overcome these limitations we first construct a 3d a priori p and s velocity model integrating known geophysical and geological information significant progress has been achieved in the 3d numerical modelling of complex geological structures by the development of dedicated softwares e g 3d geomodeller capable at once of elaborating a 3d structural model from geological and geophysical constraints and possibly of refining it by inversion processes calcagno et al 2008 then we build an arrival time catalogue of 1500 events recorded from 2000 to 2011 hypocentres are then located in this model using a numerical code based on the maximum intersection method font et al 2004 updated by theunissen et al 2012 as well as another 3d location technique the nonlinloc software lomax and curtis 2001 the reduction of arrival time residuals and uncertainties dh dz with respect to classical 1d locations demonstrates the improved accuracy allowed by our approach and confirms the coherence of the 3d geological model built and used in this study our results are also compared with previous works that benefitted from the installation of dense temporary networks surrounding the studied epicentre area the resulting 3d location catalogue allows us to improve the regional seismic hazard assessment more particularly in the south of the argentera massif and in the ligurian basin

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

southern ocean pliocene paleotemperature variation from high resolution silicoflagellate biostratigraphy abstract applying the modern biogeographic distribution of silicoflagellate genera dictyocha and distephanus and calcareous nannoplankton as an analog the biostratigraphic record of these phytoplankton can be used qualitatively to examine past changes in surface temperature in the southern ocean the antarctic polar frontal zone pfz is a major biogeographic barrier limiting dictyocha and calcareous nannoplankton to areas north of this zone ocean drilling project odp holes 748b and 751a on the southern kerguelen plateau 900 km south of the present location of the pfz contain expanded pliocene sections through four time intervals 4 5 to 4 2 ma hole 751a 3 7 to 3 1 ma hole 748b 3 6 to 3 5 ma hole 751a and 3 2 to 3 0 ma hole 751a three distinct peaks in dictyocha and calcareous nannofossil abundance reflect surface water warming of at least 4 c through either southward migration of the pfz or a weakening of the thermal gradient across this zone peak warming in the intervals studied is centered near 4 3 ma with other brief yet significant warming events near 4 5 4 2 and 3 6 ma cooling as a result of northward migration of the pfz or intensified thermal gradient is indicated by the absence of dictyocha and calcareous nannofossils in other stratigraphic intervals these data support previous studies indicating pliocene oceanic and climatic variability in the southern high latitudes silicoflagellate abundance patterns from hole 751a identify taxonomic relationships between several morphotypes the simultaneous appearance and proportional occurrence of five sided and four sided dictyocha specimens suggests a close relationship between these two forms distephanus crux s l and dictyocha aspera var pygmaea also show a near mutually exclusive abundance pattern in hole 751a and are similar in basal ring size and morphology indicating they are conspecific they differ only in apical structure whereby distephanus crux s l may have formed an apical bar under fluctuating environmental conditions in the early pliocene these variations in silicoflagellate architecture appear to be related to paleoenvironmental changes indicating that silicoflagellate morphology may represent a more useful paleoceanographic tool that has been noted previously

crustal structure from the ligurian sea to the northern apennines a wide angle seismic transect abstract a new wide angle seismic reflection profile 250 km long was shot along a line extending from parma in the apennines to the deepest part of the ligurian sea thirty seismic land stations lobs and 25 ocean bottom seismographs obs recorded 54 shots fired at sea the resulting 55 record sections allowed the definition of the transition from continental to oceanic crust in a geologically complex and hitherto poorly understood region the subducted continental crust beneath the northern apennines has a thickness of 40 km consisting of 30 km of igneous crust overlain by 10 km of sediments two sedimentary layers are identified with vp velocities in the range from 2 8 to 5 5 km s the igneous portion of continental crust thins gradually to approx 11 km across a 120 km wide zone extending from the southwestern part of the apennines some 20 km inland into the ligurian sea an easterly thinning low velocity body 7 2 7 5 km s immediately beneath the base of the crust is interpreted as an underplated unit emplaced prior to the onset of seafloor spreading this may have been initiated by magmatic activity along the incipient continental oceanic boundary a basement high coincides with the northeastern edge of the ligurian sea and is interpreted as part of the alpine ophiolite belt indicating strike slip motion the two sedimentary layers above the transition zone are typically 5 km thick and have slightly lower velocities than those further to the northeast a sharp continent ocean break is recognised in the ligurian sea oceanic crust is 6 7 km thick and is overlain by a two layered sedimentary succession approx 5 km thick mantle velocities in the region range from 7 9 km s beneath the thinned crust to 8 1 km s beneath the thick crust the ratio c o of continental to oceanic crustal thickness at the continent ocean transition is approx 1 5 and the overall crust stretching factor at that boundary is approx 3 5 these values are similar to other continent ocean boundaries and indicate that the oceanic crust in the ligurian sea formed largely by stretching with a small pull apart component

regional assessment of mass failure events in the baie des anges mediterranean sea abstract pliocene and quaternary surficial sediments of the baie des anges are commonly affected by instability laboratory analyses of sediment samples provide information about the physical properties of these sediments including consolidation state and mechanical behaviour some of these physical properties specifically undrained shear strength values s u have been calibrated by a few in situ measurements the results show that sediments deposited on the slope and on the shelf are mainly homogeneous silty clays whereas those deposited on the floor of canyons are coarser possible grain flow deposits by using s u measurements we have classified the silty clays into four geotechnical types and constructed a geotechnical map of undrained slope stability analysis infinite slope analysis provides an assessment of the possible instabilities under both drained and undrained conditions a regional hazard offshore map is presented including areas sensitive to earthquake induced sliding two potential types of failure are likely to occur in the bay shallow failures which are low volume slides involving underconsolidated near surface sediments and deeper failures which may occur on the flanks of the ridges and may be preferentially triggered by earthquakes these sliding processes involve a large volume of normally consolidated or overconsolidated sediments and may evolve into turbidity currents such as the 1979 nice slide even if it was not an earthquake induced slide channelled by the var or the paillon canyons for more than 100 km our study indicates that future development projects within the baie des anges must address offshore hazards

crust and upper mantle models along the active tyrrhenian rim the volcanic complexes from the eolian islands to the campania roman regions and tuscany further north rest on lithospheric sectors which overlie the adriatic continental lithosphere sinking along the apennine maghrebian orogenic belt evidence for this stems from the melting at mantle depth of upper crustal materials as indicated by the widespread interaction of s type and k alkaline melts the genesis of atypical magmas of the roman province central southern italy appears to be the result of an important block faulting and deep lithospheric rifting of the apennine continental margin lying parallel to and above relic sinking slabs intermediate and deep focus earthquakes indicate that the lithospheric slab is still seismically active under the eolian calabrian area and sporadically at the southern end of campania on the other hand in the roman tuscan region it seems to be almost inactive few earthquakes having been located with hypocentral depths not exceeding 150 km the analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of tuscany and south tyrrhenian sea which are separated by a tensional region which extends from latium to calabria the existence of distinct lithospheric slabs along the tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as p wave residuals and is confirmed by the trend of long wavelength gravity anomalies bidimensional gravity models along transects in the tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above mentioned lithospheric slabs

late oligocene to recent episodes of magmatism in and around the tyrrhenian sea implications for the processes of opening in a young inter arc basin of intra orogenic mediterranean type abstract five episodes of magmatic activity as deduced from geochronological data affected the tyrrhenian and peri tyr rhenian areas from the late oligocene 32 ma to recent times the episodes of w e migration of magmatism from the islands of sardinia and corsica to the eolian islands and the roman comagmatic region of central italy are related to the anti clockwise drift movements of the apenninic chain and clockwise drifting of the sicilian part of the maghrebian chain magmatic activity in the tyrrhenian sea initiated in late miocene times 8 5 6 5 ma in concomitance with a significant change of the geodynamic regime from compressional to tensional the tyrrhenian bathyal plain was affected by two episodes of spreading the first episode occurred around 7 ma and the second from about 1 9 to 1 3 ma these spreading events apparently developed during times of magmatic quiescence in the peri tyrrhenian areas two subsequent episodes of volcanism of the seamount type occurred in the bathyal plain one from 5 to 1 8 and the other from 1 3 to recent they are contemporaneously with extensive manifestations in the peri tyrrhenian areas the different types of magmatism of the late miocene back arc spreading in the central bathyal plain and acidic manifestations of intra crustal anatectic origin in the northern continental platform and slope i e islands of capraia elba and montecristo and seamount vercelli are possibly related to movements of upwelling of the astenosphere which in the southern tyrrhenian sea developed with a much stronger intensity timing of the volcanism in relationship with the overall structural evolution through time in the basin and neighbouring lands is considered

neogene history of the deep western boundary current at rekohu sediment drift southwest pacific odp site 1124 abstract odp site 1124 located 600 km east of the north island of new zealand records post middle oligocene variations in the pacific deep western boundary current dwbc and new zealand s climatic and tectonic evolution sediment parameters such as terrigenous grain size flux magnetic fabric and non depositional episodes are used to interpret dwbc intensity and antarctic climate interpretations of dwbc velocities indicate that the antarctic circumpolar current reached modern intensities at 23 ma as the tectonic seaways expanded completing the thermal isolation of antarctica periods of more intense bottom water formation are suggested by the presence of hiatuses formed under the dwbc at 22 5 17 6 16 5 15 and 14 11 ma the oldest interval of high current intensity occurs within a climatically warm period during which the intensity of thermohaline circulation around antarctica increased as a result of recent opening of circum antarctic gateways the younger hiatuses represent glacial periods on antarctica and major fluctuations in the east antarctic ice sheet whereas intervals around the hiatuses represent times of relative warmth but with continued current activity the period between 11 to 9 ma is characterized by conditions surrounding a high velocity dwbc around the time of the formation and stabilization of the west antarctic ice sheet the increased terrigenous input may result from either changing antarctic conditions or more direct sediment transport from new zealand the pacific dwbc did not exert a major influence on sedimentation at site 1124 from 9 ma to the present the late miocene to pleistocene sequence is more influenced by the climatic and tectonic history of new zealand despite the apparent potential for increased sediment supply to this site from changes in sediment channeling increasing rates of mountain uplift and volcanic activity terrigenous fluxes remain low and constant throughout this younger period

from collisional to rifted basins an example from the southern calabrian arc italy structural interpretation of available geological and geophysical data carried out along a regional transect extending across the southern calabrian arc from the tyrrhenian margins to the ionian off shore demonstrates that a complex interplay between compressional and extensional processes has controlled the evolution of upper miocene pleistocene sedimentary basins developing in this region our data indicate that an upper miocene lower pliocene succession outcropping in the southern calabrian arc represents the infilling of perched basins developed between crystalline basement thrust sheets a similar tectonic pattern characterises the plio pleistocene basins occurring on the frontal part of the arc in the ionian off shore upper pliocene pleistocene sediments outcropping along the tyrrhenian side of the arc reveal that they in fact represent the infilling of extension related basins time space migration of compressional and extensional related sedimentary basins can be explained as the result of different tectonic processes developing on the upper plate as a result of the underplating of the ionian domain beneath the calabrian block in this framework upper miocene lower pliocene and upper pliocene pleistocene perched basins represent therefore fore arc basins developed on the frontal accretionary wedge and or on the hangingwall buttress of the arc during its southeastwards migration late pliocene early pleistocene extensional tectonics occurring along the tyrrhenian side of the arc may indeed be related to accommodation processes which characterised the rear of the wedge to maintain a stable geometry as a result of the underplating of the ionian crust

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

structural framework and crustal characteristics of the sardinia channel alpine transect in the central mediterranean abstract the submerged area located between the sardinia channel and the western sicily offshore has been investigated based on deep crustal and conventional seismic lines with the aim of illustrating the relationships between the crust and its overlying crystalline and sedimentary thrust wedge analyses of seismic attributes and reflector pattern supported by dredge hauls also provided data in areas where stratigraphic and lithologic control is absent crustal geometries tectonic processes and timing of the deformation are discussed here north of the elimi chain central sardinia channel the reflecting body consists of superposed tectonic wedges of crystalline rocks and their meso cenozoic carbonatic and terrigenous cover sardinian and kabilian calabrian units the kabilian calabrian units overthrust the maghrebian apenninic units along the drepano thrust front elimi chain which is traceable on land in eastern sicily nebrodi peloritani mountains this lineament roots on the crustal mantle discontinuity where the local superposition of two different crusts occurs the thrust front of the crystalline kabilian calabrian units marks the boundary between thick skinned and thin skinned tectonics in the chain the apenninic segment of the chain develops between the elimi sector and the sciacca offshore south west sicily the crust is not as thick as expected in alpine chain areas suggesting pre orogenic thinning of the african continental crust the accretionary wedge is a southeast vergent embricate fan consisting of four groups of thrust units formed by carbonate basinal and platform ramps with duplex geometries the mesozoic carbonate units are detached from the crystalline basement not involved in the deformation the tertiary terrigenous rocks are their roof thrust the upper miocene clastic terrigenous successions sealing most of the structures appear in turn detached and piled up the intramountain plio pleistocene basins display tectonic features that point out the area underwent both extensional and contractional tectonics

early pliocene paleoenvironment of the sorsdal formation vestfold hills based on diatom data abstract comparison of diatom data from modern surface sediments in prydz bay and the kerguelen plateau with diatom assemblages from the sorsdal formation vestfold hills indicates that the climate was warmer than present during the early pliocene 4 5 4 1 ma extant sea ice associated diatoms are significantly less abundant throughout the sorsdal formation than in the modern antarctic coastal zone extant diatoms in the sorsdal formation including stellarima stellaris thalassiosira oliverana fragilariopsis sublinearis pseudo nitzschia turgiduloides and eucampia antarctica var recta are consistent with annual sea surface temperatures sst of between 1 8 and 5 0 c the presence of s stellaris indicates that the summer ssts were 3 c during some intervals the absence of calcareous coccoliths and the silicoflagellate dictyocha suggests that the upper limit for summer sst was chaetoceros cysts infer that stratified open water conditions were present during summer spring ice sheet models suggest that warming of the magnitude evident in the sorsdal formation 3 c should have resulted initially in increased snow accumulation and ice sheet growth however ice sheet growth was probably short lived as the long term response to this warming in the early pliocene resulted in a significant decrease in ice volume and deposition of the sorsdal formation other factors such as increased basal ice sliding and higher discharge icebergs and melt water probably led to significantly elevated ablation rates from the pliocene ice sheet resulting in ice sheet retreat

patterns and processes of sediment dispersal on the continental slope off nice se france the distribution of surficial sediments and sediment dispersion patterns on the steep continental slope off nice se france have been studied using side scan sonar 3 5 khz profiles short piston cores and bottom photographs the input of terrigenous material to the baie des anges a submarine embayment bounded by two prominent ridges is dominated by fluvial input from the var river the paillon river being only a minor source the var river provides very coarse bedload material gravel and cobble directly to the head of the var canyon gravel and cobble deposits are found all along the var canyon and the upper fan valley of the var submarine fan and have been shaped into gravel waves the fine particles suspension load are separated from the coarse bedload upon entering the sea and form up to 60 m thick deposits on the uppermost continental slope of the baie des anges these deposits are formed by settling out of sediment plumes the presence of silt and fine sand laminae that decrease in thickness and frequency away from the var river mouth indicate the influence of meso and hyperpycnal flows on these plume deposits areas outside the baie des anges are not connected to major fluvial input and receive only hemipelagic sediments these primary deposits are highly unstable and sediment failure due to seismic loading sedimentary loading or undercutting is frequent sediment failure produces secondary sediment gravity flows that export most of the material to the basin but also produce turbidity current over spill deposits on ridges bounding the slope canyons and on terraces within the var canyon slump and debris flow deposits are also observed at least some of these secondary flows erode the continental slope as cross cutting chutes on the upper continental slope and erosional scours in the upper fan valley demonstrate modern sediment dispersal patterns on the continental slope off nice are proposed as a modern analogue to lowstand conditions on continental margins in fact the absence of a continental shelf together with a steep slope strongly reduces the influence of sealevel on the physiography of the margin

partitioning of eolian and hemipelagic sediment in eastern equatorial pacific core tr 163 31b and the late quaternary paleoclimate of the northern andes abstract we apply simple eolian hemipelagic mixing model to characterize the terrigenous sediment component in well dated deep sea core tr163 31b raised from south of the carnegie ridge 300 km west of the coast of ecuador the terrigenous component forms 11 19 of the sediment in this pelagic core the relative amount of hemipelagic and eolian material was determined by comparison of the 1 30 m grain size distribution of the terrigenous fraction to that from a mixing model constructed from eolian and hemipelagic end members results indicate that hemipelagic deposition dominated this region from approximately 21 5 to 28 ka 14c age and 15 to 17 5 ka that both components are important from 17 5 to 21 5 ka and that the eolian component dominated sediment younger than 15 ka this depositional pattern generally matches the paleoclimatology of the northern andes specifically cooler and wetter conditions during stadials and warmer and drier conditions during interstadials and the holocene