scattering of vhf radio waves from within the top 700 m of the antarctic ice sheet and its relation to the depositional environment a case study along the syowa mizuho dome fuji traverse

two phase orogenic convergence in the external and internal sw alps the nw se trending sector of the sw alps includes the dora maira massif where tertiary eclogites record ultrahigh pressures and rapid exhumation along a ne sw crustal cross section italy france compiled pressure temperature time data in internal zones are correlated with tertiary stratigraphy in external zones to reconstruct orogen evolution revealing a coherent two phase convergence history during the first subduction accretion phase eocene 55 34 ma rapid north south plate convergence caused the subduction and exhumation of high pressure and ultrahigh pressure uhp rocks in a steady state subduction channel this coincided with the north to nnw migration of an underfilled flexural basin across the european foreland nappe stacking within the subduction channel did not create significant relief implying that primarily subduction forces generated this flexural basin from 34 ma onward the second collisional phase was characterized by slower nw se plate convergence the internal units of the sw alps underwent considerable anticlockwise rotation as they became involved in a nw se oriented sinistral transpression zone between the european and adriatic plates to the north of the orogen the north alpine foreland basin became overfilled as a result of high sediment supply from increasing orogen relief in contrast in se france active flexure of the european plate appears to have ceased and sedimentation became limited to small thrust sheet top basins created by continuing gentle ne sw shortening internal units were exhumed slowly from depths of c 20 km principally by erosion in the sw alps the transition between these two phases was marked by the rapid subduction and exhumation of the dora maira uhp unit assuming lithostatic pressure this unit would have been exhumed from 100 km depth requiring a rate that exceeds that generated by plate convergence therefore either exhumation was accelerated by additional stresses locally generated by transpression slab breakoff or high density contrasts or more controversially the ultrahigh pressure occurred at a considerably shallower depth as a result of local overpressure

the record of the messinian salinity crisis in the tertiary piedmont basin nw italy the alba section revisited abstract the alba succession tertiary piedmont basin nw italy preserves the northernmost record of the messinian salinity crisis msc and was deposited on the southern margin of a wide wedge top basin related to the involvement of the piedmont basin in the apennine compressional tectonics pre msc sediments consist of a cyclic succession of marine euxinic shales and calcareous marls deposited under the influence of precession modulated climate changes and document the progressive restriction of the basin prior to the onset of the msc they are followed by the primary lower gypsum unit plg deposited during the first msc stage from 5 96 to 5 60 ma these sediments show a clear precession related cyclic stacking pattern and record the lateral transition from a shallow water marginal setting in the sw to a deeper one in the ne in marginal settings six plg cycles are recognised truncated by an erosional unconformity placed at the base of the post evaporitic sediments the lowermost five cycles are composed of massive and banded selenite beds separated by thin shale intervals a sharp change evidenced by the appearance of the branching selenite facies is recorded by the 6th gypsum bed that represents a distinctive marker bed here called sturani key bed that can be mapped throughout the study area basinward the lower plg cycles are transitional to decimetre thick carbonate rich layers interbedded to euxinic shales that are overlain by the sturani key bed above the marker bed other seven plg cycles are present the gypsum beds form thinner bodies compared to the sturani key bed and are characterised by a greater amount of fine grained terrigenous fraction suggesting an increase of continental runoff related in turn to humid climate conditions at the end of the first msc stage plg cycles are followed by slumped mudstones and clastic gypsum beds that correspond to the resedimented and chaotic facies resedimented lower gypsum deposited in the mediterranean basins during the second msc stage from 5 60 to 5 55 ma they are in turn overlain by continental and brackish water facies with lago mare fossil assemblages recording the final stage of the msc the messinian succession of alba provides the opportunity to reconstruct the lateral facies transition between marginal and distal settings and to shed new light on the deep water msc sedimentary record moreover the appearance of the branching selenite facies from the 6th plg cycle upward provides a tool for properly placing the piedmont record in the msc chronostratigraphic framework allowing us to investigate the influence of climate gradients on the sedimentary response to the mediterranean salinity crisis

modeling the radio echo reflections inside the ice sheet at summit greenland 1 radio echo surveys to determine the thickness of ice sheets often record reflections from inside the ice to increase our understanding of these internal reflections we have used synthetic seismogram techniques from early seismic modeling to construct two models both models were one dimensional the first considered only primary reflections while the second included both primary and multiple reflections the inputs to both models were a radio pulse and data from the greenland ice core project grip core of length 3028 m the ice core data consisted of a profile of the high frequency conductivity calculated from dielectric profile dep measurements and a smooth profile of the real permittivity the models produced synthetic radargrams which are the energy reflected from conductivity variations as a function of the two way travel time both models gave similar results indicating that multiples do not alter the travel time of the reflections i e no o doherty anstey effect at our time resolution one of the results was then processed to simulate the reflected energy passing through the receiver circuit of a radio echo system and then compared with a recorded trace the processed result contained many of the larger reflections recorded below about 500 m including nearly all the features from depths greater than 1500 m in particular several interstadial events in the wisconsin age ice since high frequency conductivity variations are dominated by chemical changes which are caused by deposition on the surface of the ice sheet it is possible to conclude that the reflections deep inside the greenland ice sheet can be treated as isochrons

crustal structure of northern italy from the ellipticity of rayleigh waves abstract northern italy is a diverse geological region including the wide and thick po plain sedimentary basin which is bounded by the alps and the apennines the seismically slow shallow structure of the po plain is difficult to retrieve with classical seismic measurements such as surface wave dispersion yet the detailed structure of the region greatly affects seismic wave propagation and hence seismic ground shaking here we invert rayleigh wave ellipticity measurements in the period range 10 60 s for 95 stations in northern italy using a fully non linear approach to constrain vertical v s v p and density profiles of the crust beneath each station the ellipticity of rayleigh wave ground motion is primarily sensitive to shear wave velocity beneath the recording station which reduces along path contamination effects we use the 3d layering structure in mambo a previous model based on a compilation of geological and geophysical information for the po plain and surrounding regions of northern italy and employ ellipticity data to constrain v s v p and density within its layers we show that ellipticity data from ballistic teleseismic wave trains alone constrain the crustal structure well this leads to mambo e an updated seismic model of the region s crust that inherits information available from previous seismic prospection and geological studies while fitting new seismic data well mambo e brings new insights into lateral heterogeneity in the region s subsurface compared to mambo it shows overall faster seismic anomalies in the region s quaternary pliocene and oligo miocene layers and better delineates the seismic structures of the po plain at depth two low velocity regions are mapped in the mesozoic layer in the western and eastern parts of the plain which seem to correspond to the monferrato sedimentary basin and to the ferrara romagna thrust system respectively

oligocene to present kilometres scale subsidence and exhumation of the ligurian alps and the tertiary piedmont basin nw italy revealed by apatite u th he thermochronology correlation with regional tectonics the ligurian alps segment of the alpine apennine orogen in nw italy is unconformably covered by upper eocene to holocene sediments in the tertiary piedmont basin tpb and po plain these sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin apatite u th he and fission track thermochronology shows that the orogen first subsided and was buried at 4 km from 30 to 26 ma and began its exhumation thereafter from 26 ma to present this upward movement was contemporaneous with subsidence in the northern tpb the couple exhumation in the s and subsidence in the n migrated northwards through time vertical movements in the area are similar to those reconstructed in corsica in both cases the onset of exhumation b

a new perspective on sequence stratigraphy of syn orogenic basins insights from the tertiary piedmont basin italy and implications for play concepts and reservoir heterogeneity

the thick bedded tail of turbidite thickness distribution as a proxy for flow confinement examples from tertiary basins of central and northern apennines italy this study reviews the thickness statistics of non channelized turbidites from four tertiary basins of central northern apennines italy where bed geometry and sedimentary character have been previously assessed though very different in terms of size and arguably character of feeder system these basins share a common stratigraphic evolution consisting in transition from an early ponded to a late unconfined setting of deposition based on comparison of thickness subsets from diverse locations and stratigraphic heights within the studied turbidite fills this paper seeks to answer the following questions i how data collection procedures and field operational constraints e g measure location outcrop quality use of thicknesses data from single vs multiple correlative sections stratigraphic thickness of the study interval can affect statistics of sample data ii how depositional controls of confined vs unconfined turbidite basins can result in different thickness frequency distributions and iii is there in thickness statistics a flow confinement signature which can be used to distinguish between confined and unconfined turbidites results suggest that i best practices of data collection are crucial to a meaningful interpretation of sample data statistics especially in presence of stratigraphic and spatial trends of turbidite bed thickness ii a systematic bias against cm thick tcd bouma sequence turbidites exists in sample data which can result in the low end tail of empirical thickness frequency distributions to depart significantly from the actual distribution of turbidite thickness and iii thickness statistics of beds starting with a basal ta tb bouma division bear a coherent relationship to the transition from ponded to unconfined depositional settings consisting in reduction of variance and mean and consequently parameters or even type of best fit model distribution this research highlights the role of flow stripping sediment by pass and bed geometry in altering the initial thickness distribution of ponded turbidites and suggests how fully ponded mini basins represent the ideal setting for further research linking turbidite thickness statistics and frequency distribution of parent flow volumes

modeling the evolution of antarctic ice sheet over the last 420 000 years implications for altitude changes in the vostok region a new thermomechanical three dimensional model designed to simulate the evolution of the antarctic ice sheet over long time periods is presented this model incorporates the various types of ice flow found in antarctica relatively slow inland ice flow that is essentially due to ice deformation fast ice flow in the regions with ice streams and ice shelf flow by coupling these three types of flow it is possible to predict grounding line migration simulations covering four glacial interglacial cycles have been conducted by forcing this model with a temperature record from vostok and a sea level record from marine cores our findings indicate that grounding line migration induced by sea level changes is the primary factor governing the evolution of the antarctic ice volume on the other hand the altitude of the ice sheet surface at vostok is driven by accumulation rate variations the amplitude of the altitude change does not exceed 150 m and is very similar for all the sites located on the antarctic plateau

magnetochronology applied to assess tempo of turbidite deposition a case study of ponded sheet like turbidites from the lower miocene of the northern apennines italy abstract this paper investigates the magnetostratigraphy of the 750 m thick costa grande member lower miocene from the castagnola basin of nw italy which represents the turbidite fill of a structurally confined basin where flow ponding resulted in a complete record of deposition from diverse sediment gravity flow types the magnetostratigraphic profile of the costa grande mb was correlated to the geomagnetic polarity timescale using a well established statistical method devised to be applied to sedimentary successions with steady accumulation rate the results of the correlation exercise validated with the available biostratigraphy indicate an early miocene age from chron c6aar 3r to c6bn 2n between 21 7 and 22 3 ma the obtained age model was then used to calculate accumulation rates and frequencies of small volume and low density vs large volume and high density gravity flows over an estimated 650 kyr time span results show that low density flows contributed at a constant pace of 545 m myr 1 to sediment accumulation depositing relatively thin bedded turbidites with a minimum recurrence time of 1 7 kyr whereas the high density flows which are at least four times less frequent are clustered in the stratigraphy and become more abundant up section we also show that the minimum sediment volumes discharged by high density flows suggest triggering by submarine failures whose recurrence and magnitude were probably not random lastly we propose that the statistical method used in this study to correlate the costa grande mb magnetostratigraphy to the gpts provides best results when the products of episodic but voluminous depositional events are carefully identified and removed

unravelling polyphase brittle tectonics through multi software fault slip analysis the case of the voltri unit western alps italy abstract we have analyzed the brittle structures in a key area of the alps apennines transition zone nw italy here two orogens have interfered with each other since oligocene times producing a complex structural evolution and a heterogeneous fault population only relative chronologies can be reconstructed as stratigraphic constraints are lacking we have performed the inversion of fault slip data with two softwares for paleostress calculations combined with field observations at selected structural stations and photo interpretation the resulting incompatible stress tensors can be grouped in this sequence i a strike slip tensor with nnw sse trending 1 event a ii a strike slip tensor with ne sw trending 1 event b and iii an extensional transtensional tensor with nw se or ne sw trending 3 event c we correlated our results with structures of known age from adjacent areas event a is possibly rupelian early chattian linked to far field incipient rifting in the future ligurian provencal basin event b fits oligo miocene shortening the faults may belong to a sinistral strike slip zone that accommodated the oblique component of deformation during the rotation of the corsica sardinia block event c is attributed to a pliocene quaternary neotectonic event therefore combining different inversion procedures with a detailed structural analysis has successfully unravelled the polyphase brittle tectonics

provenance of oligocene synorogenic sediments of the ligurian alps nw italy inferences on belt age and cooling history mineral chemistry 40ar 39ar geochronology on white micas and apatite fission track thermochronology aftt are applied here to study the provenance of the synorogenic molare formation lowermost unit of the tertiary piedmont basin clastic sequence the molare formation was deposited during transgression onto the ligurian alps nappe stack in the early oligocene depositional facies show that clastic distribution remained transversal with local sources located just landward from the coastline phengite mineral chemistry together with 40ar 39ar data clearly shows two distinctive source areas each one mirroring the composition of the basement directly beneath the clastic sequence amphibole mineral chemistry allows second order provenance distinctions within each sector reflecting heterogeneous metamorphic evolution of the bedrock complexes integrated 40ar 39ar dating and aftt suggest that following a fast cooling exhumation episode of the ligurian alps during the oligocene very little net uplift has since occurred this is due to a period of general subsidence from the oligocene late miocene followed by comparable uplift from late miocene pliocene to the present in general our data provide an image of the ligurian alps during the oligocene which is very similar to the present day one

late stages of exhumation constrained by structural fluid inclusion and fission track analyses sesia lanzo unit western european alps in metamorphic areas paleogeothermal gradients are difficult to properly estimate leading to great uncertainty in exhumation rate calculations based on fission track analysis in this work a new multidisciplinary approach based on fluid inclusion analysis structural analysis and fission track dating has proven to be able to constrain the late stages of exhumation of metamorphic rocks the study area is located in the sesia lanzo unit of the western european alps along the hone shear zone kinematic analysis at different scales unraveled a polyphase postmetamorphic deformation history constrained in the p t space thanks to laboratory investigation of kinematically referenced fluid inclusions coupled with the analysis of the rheological behavior of quartz and feldspar inside syn kinematic veins the resulting p t path points to an increasing paleogeothermal gradient from 18 to 30 c km 1 after greenschist facies metamorphic conditions and provides a reference framework for a quantitative interpretation of fission track data in terms of exhumation rates and fault throws according to fission track data throws accommodated by the hone shear zone between 33 and 30 ma are on the order of 4 5 km and would be underestimated by 25 if a normal steady gradient was assumed for the whole post metamorphic history of the area the deepest portions of this structure were exhumed thanks to the activity of the e w fault system that accommodated a throw of 4 km between 28 and 20 ma and a throw of 0 8 km during the last 20 myr

messinian carbonate rich beds of the tertiary piedmont basin nw italy microbially mediated products straddling the onset of the salinity crisis abstract the seven messinian microbial carbonate rich layers cropping out in the pollenzo section tertiary piedmont basin nw italy are interbedded with a precession related cyclic succession composed of euxinic shale marl couplets and straddle the onset of the messinian salinity crisis msc a sharp change of sedimentological compositional and geochemical characteristics was observed from the onset of the msc onward suggesting strong differences in the mechanisms responsible for carbonate precipitation pre msc beds are mainly composed of dolomite and are interpreted as the product of early diagenesis formed by bacterial sulphate reduction in the shallow subsurface along the sulphate methane interface dolomite precipitation was temporarily enhanced by an upward flux of methane rich fluids possibly sourced by gas hydrate destabilisation conversely from the onset of the msc onward carbonate beds are thinly laminated and show abundant filaments interpreted as beggiatoa like bacteria while calcite and aragonite are the dominant authigenic phases these beds are interpreted as microbialites resulting from the lithification of chemotrophic bacterial mats dominated by sulphide oxidizing bacteria the carbonate necessary for their preservation was provided by bacterial sulphate reduction these microbialites that appear as the deeper water counterpart of bottom grown selenite layers deposited in the marginal part of the basin formed on an anoxic sea bottom under a density stratified water column the high sulphate concentration in the pore waters related to the presence of concentrated brines and to the regeneration of sulphate by sulphide oxidizing bacteria is considered as the driving factor controlling the mineralogical change from dolomite to calcite and aragonite finally the sharp shift towards negative 18 o values of carbonates observed from the onset of the msc onward was probably related to fractionation processes operated by sulphate reducing bacterial communities in the pore waters this suggests that care must be taken when dealing with microbial carbonates in the interpretation of the oxygen isotope values in terms of fluctuating salinity condition of the water mass in conclusion this study suggests that the onset of the msc had a strong impact on microbial populations governing carbonate precipitation in a sector of the basin dominated by depositional conditions not suitable for gypsum precipitation

the collisional knot in liguria a series of 8 new seismic refraction profiles were computed as extensions of the borehole controlled reflection profiles of the po plain into the northern apennines and the ligurian alps they help to more clearly define the subsurface structure of this intricate ligurian knot in particular it has been possible to identify a number of high velocity bodies and they may be correlated with such geological entities as the adriatic mesozoic ophiolites of the apenninic liguride nappes and ophiolites or mesozoic carbonates underlying the antola flysch in the alpine part of the knot when combining the refraction and reflection lines these bodies appear to be bounded by important dislocation surfaces such as the padanide sole thrust plio pleistocene the villalvernia varzi line oligo miocene the ottone levanto line oligo miocene and the volpedo valle salimbene fault oligo miocene reactivated as a transfer fault in the plio pleistocene the 3d geometry may be interpreted in terms of regional kinematics and is compatible with a model that envisages an oligo early miocene nw translation of the adriatic indenter coupled with collapse in the provencal ligurian sea and rotation of the sardinia liguria complex into the roll back of the adriatic subduction zone the refraction interpretations extending to a depth of 15 km are supplemented by data on the moho configuration obtained for the european geotraverse the moho appears to be dissected into a series of patches which may be interpreted in terms of the shallow crustal configuration and its history in particular the deepest patch appears to be terminated by the volpedo valle salimbene fault which consequently would displace the entire crust

an improved coherent radar depth sounder the university of kansas developed a coherent radar depth sounder during the 1980s this system was originally developed for glacial ice thickness measurements in the antarctic during the field tests in the antarctic and greenland we found the system performance to be less than optimum the field tests in greenland were performed in 1993 as a part of the nasa program for arctic climate assessment parca we redesigned and rebuilt this system to improve the performance the radar uses pulse compression and coherent signal processing to obtain high sensitivity and fine along track resolution it operates at a center frequency of 150 mhz with a radio frequency bandwidth of about 17 mhz which gives a range resolution of about 5 m in ice we have been operating it from a nasa p 3 aircraft for collecting ice thickness data in conjunction with laser surface elevation measurements over the greenland ice sheet during the last 4 years we have demonstrated that this radar can measure the thickness of more than 3 km of cold ice and can obtain ice thickness information over outlet glaciers and ice margins in this paper we provide a brief survey of radar sounding of glacial ice followed by a description of the system and subsystem design and performance we also show sample results from the field experiments over the greenland ice sheet and its outlet glacicrs

three dimensional radar imaging of structures and craters in the martian polar caps abstract over the last decade observations acquired by the shallow radar sharad sounder on individual passes of the mars reconnaissance orbiter have revealed the internal structure of the martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate however a complete picture of the cap interiors has been hampered by interfering reflections from off nadir surface features and signal losses associated with sloping structures and scattering foss et al the leading edge 36 43 57 2017 https doi org 10 1190 tle36010043 1 addressed these limitations by assembling three dimensional data volumes of sharad observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously the radar volumes provide unprecedented views of subsurface features readily imaging structures previously inferred from time intensive manual analysis of single orbit data e g trough bounding surfaces a buried chasma and a basal unit in the north massive carbon dioxide ice deposits and discontinuous layered sequences in the south our new mapping of the carbon dioxide deposits yields a volume of 16 500 km 3 11 larger than the prior estimate in addition the radar volumes newly reveal other structures including what appear to be buried impact craters with no surface expression our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a hesperian age for the substrate consistent with that of the surrounding plains as determined from statistics of surface cratering rates planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits the radar volumes also provide new topographic data between the highest latitudes observed by the mars orbiter laser altimeter and those observed by sharad in general mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes

post collisional tectonics in the northern cottian alps italian western alps field mapping and structural analysis have allowed us to characterise the fault geometry and the post metamorphic tectonics of an area located in the northern cottian alps inner western alps two main faulting stages were distinguished here the first oligocene early miocene is related to the development of an e w striking left normal shear zone this shear zone is interpreted as an antithetical of two regional n s right lateral structures the col del lis trana deformation zone ltz and the colle delle finestre deformation zone cfz the second faulting stage post early miocene is related mainly to the development of n s normal faults coeval with the extensional reactivation of the ltz and the cfz we discuss this kinematic evolution in the framework of the geodynamic evolution of the western alps

ice flow physical processes derived from the ers 1 high resolution map of the antarctica and greenland ice sheets accepted 1999 july 7 received 1999 june 7 in original form 1998 june 24 summary the ers 1 satellite launched in 1991 has provided altimetric observations of the greenland ice sheet and 80 per cent of the antarctica ice sheet north of 82 s it was placed in a geodetic 168 day repeat orbit between april 1994 and march 1995 yielding a 1 5 km across track spacing at latitude 70 with a higher along track sampling of 350 m we have analysed the waveform altimetric data from this period to compute maps with a 1 30 grid size data processing consists of correcting for environmental factors and editing and retracking the waveforms a further step consists of reducing the radial orbit error through crossover analysis and correcting the slope error to second order the high resolution topography of both ice sheets reveals numerous details a kilometre scale surface roughness running at 45 from the flow direction is the dominant topographic characteristic of both continents antarctica also exhibits many scars due to local flow anomalies several physical processes can be identified abrupt transitions from deformation to sliding and vice versa and impressive strike slip phenomena inducing en echelon folds

structural control on karst water circulation and speleogenesis in a lithological contact zone the bossea cave system western alps italy abstract geological surveys structural mapping and thin section analysis helped to unravel the speleogenesis and water circulation in the bossea cave northern italy an unconventional karst system at the contact between carbonates and underlying insoluble rocks the surveys within the cave and in the surrounding surface outcrops revealed a complex structural setting caused by the coupling of lithological mechanical heterogeneities with two major regional left lateral ese wnw strike slip faults transpression associated with the faults led to a disharmonic deformation accommodated by a detachment surface between the buckled basement meta volcanics and the disharmonically folded marble sequence laying on top low angle shear zones recumbent or drag folds and small stacks of duplexes are localized next to this detachment the preferential pathways for water circulation inside the vadose zone are the folded bedding interfaces in the meta carbonate sequence fracture clusters at slipping bed terminations on the other hand provide through sequence connectivity once underground stream water flow reached the cataclastic and highly deformed meta volcanics of the detachment core and damage zones erosion started removing large volumes of rocks the downward erosion of the permian basement rocks caused gravitational instability and subsequent roof collapses aided by structural control in the damage zone above the detachment surface slip surfaces in between duplexes or drag folds this gravitational instability ultimately led to the formation of the giant halls that are characteristic of the downstream part of the bossea cave

ice flow induced scattering zone within the antarctic ice sheet revealed by high frequency airborne radar to better understand how internal radar echoes depend on ice flow conditions and radar polarization we surveyed two basins in east antarctica using 179 mhz airborne radar we compared radar echoes from three ice flow conditions parallel sheet flow in the main stream of a basin convergent flow towards an ice stream and longitudinal compression by nunataks we detected a distinct zone of high radar scattering several hundred meters thick at middle depths in the latter two regions this high scattering zone was detected only when the radar polarization plane was parallel to the compression axis in ice such a high scattering zone was not found in the parallel flow region regardless of the polarization using a recently developed theory of radar scattering in ice we interpret the high scattering zone as being caused by crystal orientation fabric alternations among adjacent ice layers due to difference in horizontal strain components we argue that the spatial variation of the high scattering zone is crucial for understanding past and present flow features

nutrient influence on fossil carbonate factories evidence from sedex extractions on burdigalian limestones miocene nw italy and s france abstract different miocene shallow water carbonate successions have been examined to test the potential of phosphorus sequential extraction sedex in studying palaeo nutrient levels and to investigate nutrient influence on carbonate factories during this epoch the coralline algal dominated sequence of the pietra da cantoni group nw italy and the bryozoan dominated sequence of the sommieres basin s france have been targeted for this study actually albeit they both developed during the burdigalian in the very same latitudinal zone they present remarkably different carbonate factories palaeontological analyses have investigated the distribution of the major groups of carbonate producing organisms throughout the successions these results have been compared with those of geochemical analyses on phosphorus and organic matter abundance testifying a clear relationship between the skeletal assemblage and the availability of nutrients as expected on the basis of modern oceanography and benthic ecology bioavailable phosphorus concentration was higher in the bryozoan dominated basin than in the coralline algal dominated basin this result strongly supports sedex sequential extraction as a viable instrument to investigate the nutrient supply in the geological record this also proves that the early miocene mediterranean carbonate factories were deeply controlled by nutrient influence with patterns similar to those observed in present day oceans moderate nutrient concentrations resulted in coralline algal dominance while high nutrient concentrations produced carbonate factories dominated by heterotrophs suspension feeders like bryozoans the euphotic zone producers which dominate in classical tropical associations were probably restricted to areas with low nutrient concentrations

a flow law for anisotropic ice and its application to ice sheets a new formulation of the flow law of polycrystalline ice was derived for an rbitrary c axis orientation fabric pattern the rate factor of the flow law is given by a geometrical factor that can be calculated with c axis fabric data and stress condition a theoretical calculation combining this flow law with a lattice rotation model by intracrystalline slip in the constituent grains predicts the development of characteristic fabric patterns observed in many laboratory experiments and in the field according to this flow model of polycrystalline ice if significant recrystallization does not occur uniaxial compression makes the ice body harder with increasing strain whereas simple shear makes the ice body softer with strain this may significantly affect ice sheet dynamics

tectonic significance of cenozoic exhumation and foreland basin evolution in the western alps the alps are the archetypical collisional orogenic system on earth and yet our understanding of processes controlling topographic growth in the cenozoic remains incomplete whereas ideas and models on the alps are abundant data from the foreland basin record able to constrain the timing of erosion and sedimentation mechanisms of basin accommodation and basin deformation are sparse we combine seismic stratigraphy micropaleontology white mica 40ar 39ar detrital zircon u th he and apatite fission track thermochronology to miocene pliocene samples from the retro wedge foreland basin saluzzo basin in italy and to oligocene miocene sedimentary rocks from the pro wedge foreland basin b rreme basin in france of the western alps our new data show that exhumation in the oligocene miocene was non uniform across the western alps topographic growth was underway since the oligocene and exhumation was concentrated on the pro side of the orogenic system rapid and episodic early miocene exhumation of the western alps was concentrated instead on the retro side of the orogen and correlates with a major unconformity in the proximal retro foreland basin a phase of orogenic construction is recorded by exhumation of the proximal pro foreland in both the central and western alps at ca 16 ma this is associated with high sedimentation rates and by inference erosion rates and suggests that an increase in accretionary flux associated with the dynamics of subduction of europe under adria controlled orogenic expansion in the miocene

late orogenic vertical movements within the arc of the sw alps and ligurian alps abstract mainly on the basis of seismic data we reconstruct magnitude and timing of miocene to present vertical movements in the region of the savigliano basin an up to 4 km thick succession of neogene to quaternary sediments accumulated inside the alpine arc at the western termination of the po plain we focus in particular on the margins of the basin which are the link between the mountain range and the subsiding basin seismic data from these regions allow for the definition of upward and downward vertical movements uplift exhumation and subsidence with a spatial and temporal resolution which cannot be attained by other methods the eastern southern and western margins of the savigliano basin display very different geometries of the sedimentary bodies and therefore document different vertical movements during miocene to present times the eastern part of the savigliano basin and the regions to the e experienced subsidence followed by exhumation the southern margin of the basin in the cuneo area was much more stable with miocene to present formations all pinching out close to the present day outcropping position of the basement sedimentary cover contact in the w seismic sections record a stage of tilting until the burdigalian followed by generalized subsidence which affected also the adjacent regions of the sw alps the overall pattern of vertical movements is essentially controlled by the nw ward migration of a syncline anticline couple with the synclinal axis presently located in the center of the savigliano basin the width of the folds is in the order of 30 60 km 1 2 wavelength in map view the trace of the fold axes changes from n s in the savigliano basin to e w in the alessandria basin

climatic and hydrologic variability in the northern mediterranean across the onset of the messinian salinity crisis abstract the youngest and one of the largest saline deposits of earth history formed in the mediterranean during the messinian salinity crisis msc 5 97 5 33 ma late miocene when global climate was experiencing a trend of cooling and aridification however recent paleoclimate reconstructions indicate strong climate gradients across the mediterranean basin and the persistence of humid conditions in the northern mediterranean during the earliest phase of the msc to characterize climatic and hydrologic variability across the onset of the msc we studied inorganic geochemical proxies comprising si ti and zr element distributions and organic geochemical proxies such as sedimentary plant wax contents and their carbon 13cn alk and hydrogen 2 n alk stable isotope compositions in deep water 200 m alternating shale and marl deposits of the piedmont basin govone section nw italy our results suggest that deposition was controlled by precession driven climate fluctuations before and after the onset of the msc with shales deposited under moister conditions lower element al ratios and 2 n alk values and marls when drier conditions prevailed higher element al ratios and 2 n alk values the observed 2 n alk pattern further suggests changes in the relative contributions of the sources of moisture for precipitation at precession minima shales were deposited and moisture was mainly sourced from the north atlantic as reflected by lower 2 n alk values at precession maxima marls were deposited and higher 2 n alk values point to a probably western mediterranean source of moisture the decrease of element al ratios as well as the coeval increase of plant wax abundances after the onset of the msc indicate enhanced humidity and increased net precipitation over the northern mediterranean these changes coincided with a restriction of the atlantic mediterranean gateways and resulted from an enhanced contribution of deuterium enriched moisture sourced from seawater evaporation in the mediterranean evidenced by an increase of 2 n alk values

single and double exhumation of fault blocks in the internal sesia lanzo zone and the ivrea verbano zone biella italy the combination of magmatic structural and fission track ft data is used to unravel oligocene miocene near surface tectonics in the internal western alps this includes reburial of parts of the already exhumed sesia lanzo zone and their subsequent re exhumation we define blocks mainly on the base of their oligocene miocene cooling history ft data and on published paleomagnetic data the preservation of a paleosurface allows a detailed reconstruction of the exhumation burial and re exhumation of different tectonic blocks near surface rigid block rotation is responsible for the reburial of the lower oligocene paleosurface in part of the sesia lanzo zone the cervo block and for the conjugate uplift of deeper portions of the ivrea verbano zone the sessera ossola block this block rotation around the same horizontal axes produces in the currently exposed portions of the two blocks quite different temperature time paths while the surface of the cervo block is buried the lower part of the sessera ossola block is uplifted the rotation is constrained between the age of emplacement of the biella volcanic suite on top of the sesia lanzo zone 32 5 ma and the intrusion of the valle del cervo pluton 30 5 ma after this relative fast movements the concerned blocks remained in or underneath the partial annealing zone of zircon until in aquitanian times they were rapidly uplifted into the partial annealing zone of apatite the further stage of exhumation out of the partial annealing zone of apatite extends over the entire miocene at that time units of the external western alps underwent fast exhumation external brianconnais valais in addition to the well known post collisional deformation in the axial and external western alps the internal units i e the upper plate hold an apparent stable position in terms of exhumation

thrusting and faulting in metamorphic and sedimentary units of ligurian alps an example of integrated field work and geochemical analyses in a sector placed in the se part of the alps apennine junction a kilometre scale shear zone has been identified as the grognardo thrust zone gtz which caused the ne directed thrusting of metaophiolites voltri group and polymetamorphic continental crust slices valosio unit of ligurian alps onto oligocene sediments of an episutural basin known as tertiary piemonte basin the structural setting of the gtz is due to syn to late metamorphic deformation followed by a brittle thrusting that occurred in the late aquitanian times and can thus be related to one of the main contractional tectonic events suffered by northern apennines the gtz was then sealed by lower burdigalian carbonate platform sediments visone formation transtensive faulting followed in post burdigalian times along nw se regional faults and displaced the previously coupled sedimentary and metamorphic units the gtz thus underwent a plastic to brittle evolution during which carbonate rich fluids largely sustained the deformation in these stages a complex vein network originated within both the metamorphic and sedimentary rocks field data and stable isotopic analyses 13c and 18o of bulk rocks and veins show that fluid rock interaction caused the carbonatisation of the rocks in the late metamorphic stages and the cataclasis and recementation by the action of isochemical cold carbonate groundwater during the thrusting events carbonate veins largely developed also during the transtensive faulting stages with composition clearly different from that of the veins associated to thrust faults as indicated by the strong depletion in 13c of carbonate fillings suggesting the presence of exotic fluids characterised by a high content of organic matter

complex bedding geometries and facies associations of the turbiditic fill of a confined basin in a transpressive setting castagnola fm tertiary piedmont basin nw italy this paper details the influence of syndepositional tectonics in controlling the architecture of a well exposed confined turbiditic sandbody which crops out in the eastern part of the tertiary piedmont basin castagnola basin northern italy the castagnola basin was tectonically active during sedimentation of the sandbody and the lateral distribution of turbidity current deposits has been used to constrain both how the basin subsided and the impact of basin topography on flow behaviour and deposition the sandbody occurs in the lower member of an upper oligocene lower miocene turbidite system the castagnola formation the sandbody is 30 m thick and can be followed laterally for 1 8 km it shows onlap terminations onto both northern and southern basin margins the outcrop is sufficiently large to allow a detailed analysis of the facies and geometrical heterogeneity as viewed approximately parallel to the average palaeocurrent trend sw ne correlation between 41 sedimentological logs reveals the diachronous development of a succession of sandstone packages subunits nine vertically stacked and laterally juxtaposed packages have been recognized subunits b to i from oldest to youngest which reflect changes in basin floor accommodation as a result of synsedimentary tectonism each package shows the development of different vertical stacking patterns with thinning and fining upward small scale sequences and variable lateral facies arrangements as a consequence of the position relative to the basin margins the geometry stratigraphic relationships facies distribution and palaeocurrent directions indicate that turbidite deposition during accumulation of most of the sandbody was controlled by 1 synsedimentary tilting of the basin slopes 2 the distribution of structural and depositional relief within the basin 3 the thickness and volume of the turbidite flows and 4 the angle of impingement of turbidity currents against the basin slopes

seismotectonic investigations in the inner cottian alps italian western alps an integrated approach abstract this work integrates the results of recent geological structural studies with new seismological data for the inner cottian alps to investigate the connection between faults and seismicity the major post metamorphic tectonic feature of this sector is represented by a n s structure named lis trana deformation zone ltz since the late oligocene this structure accommodated right lateral late oligocene early miocene and subsequently normal post early miocene displacements in the pleistocene the activity of the ltz seems to have caused the development of lacustrine basins inside the valleys that drain this sector of western alps the present day seismicity joins the northern part of the ltz and southwards other minor sub parallel structures in transversal cross section hypocentres highlight steep surfaces focal mechanisms calculated along this structure show both extensional and strike slip solutions mostly with one roughly n s striking nodal plane both sub horizontal with ne sw to ene wsw trend and steeply dipping p axes with n s to nw se sub horizontal t axes are observed even if clear evidence of quaternary tectonic activity in the area is missing on the basis of the available seismological and geological data we propose that in the inner northern cottian alps the present day seismic activity may be connected to the ltz interpreted as minor sub parallel fault strand of the canavese line the kinematics of this structure is consistent with the focal mechanisms calculated in this area structural and seismological data indicate that ltz is active under a bulk dextral transtensive regime since the late oligocene in the inner cottian alps in agreement with the data published for the adjacent domain of the chain

three dimensional seismo tectonics in the po valley basin northern italy the po valley northern italy is a composite foreland foredeep basin caught in between the southern alps and northern apennine mountain belts by integrating the 3d structural model of the region with the public earthquake dataset the seismo tectonics of the basin is shown at different scales of observation the three dimensional geo volumeis used to reviewthe seismicity around the region and validate the structure earthquake association for such a complex tectonic framework despite the overall uncertainty due to the original data distribution quality as well as the crustal scale model dimension the direct correlation between structures and seismicity a confirms the po valley region as an active tectonic system and b allows the whole structural architecture to be revised by a unique three dimensional perspective and approach this study also indicates that 3d methodology is a powerful tool for better understanding of highly complex seismo tectonic situations at both regional and local scales

the upper miocene diatomaceous sediments of the northernmost mediterranean region a lamina scale investigation of an overlooked palaeoceanographic archive

late oligocene miocene sedimentary evolution of the critical alps apennines junction the monferrato area northwestern italy the monferrato is a key area of the alps apennine junction it consists of a tertiary succession resting on apennine related units in turn overridden by the alpine basement the superficial expression of this crustal discontinuity is the rio freddo deformation zone separating the alpine related torino hill domain from the monferrato stratigraphic analyses allow the recognition of different fault bounded oligo miocene successions interpreted as tectonostratigraphic units some of these corresponded to high standing blocks others to subsiding basins the facies distribution reflects a transpressional tectonic regime in this general framework of wrench tectonics sedimentation was influenced by palaeoceanographic factors during the early and latest burdigalian while tectonics played the dominant role during the aquitanian and the late burdigalian the uniform extent and the unconformable basal boundary of the langhian deposits suggest that the different tectonostratigraphic units presently composing the monferrato area were in place by langhian times

3d crustal architecture of the alps apennines join a new view on seismic data abstract seismic data from the alps apennines join have usually been interpreted in the form of 2d cross sections passing either through the western alps or the ligurian alps monferrato apennines however the oblique se nw convergence of adria and europa and superimposed rotations imply a distinct 3d kinematic development around the adriatic indenter ai the westernmost spur of adria in order to develop kinematic models data on motion at the different margins of ai must be coordinated along the northern margin the dextrally transpressive insubric line il was active between 25 and 16 ma insubric helvetic phase of alpine orogeny contemporaneously along the southern margin paleo apenninic phase a complementary sinistral motion took place along the villalvernia varzi line vvl it emplaced the monferrato apennines westward to the north of the ligurian alps by carrying them westward on top of ai between 14 and 6 ma jura lombardic phase of alpine orogeny the lombardic thrust belt developed on the northern margin of ai now largely hidden under the po plain its continuation to the southwest is impeded by older thrust masses along the western alps that consist largely of basement their sediments having been eroded as noted on the deep reflection line crop alpi 1 by earlier investigators this line moreover contains a deep reflection band originating in the autochthonous mesozoic of the apenninic foredeep in order to better visualize this origin and the relation of further elements identified on reflection lines around the northwestern end of the monferrato apennines a 3d fence diagram was constructed it helps in establishing a 3d structural kinematic model of the alps apennines join based on the kinematics of ai this model features an underthrust of ai under the western alps in the paleo apenninic phase in the course of this underthrust the paleo apenninic elements of the monferrato moved under the marginal thrusts of the western alps subsequent neo apenninic thrusting brought both elements together to the surface where they now form the monferrato and turin hills a derivation of the alpine collina di torino from the south instead of from the west as recently proposed meets with serious kinematic difficulties

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

trophism climate and paleoweathering conditions across the eocene oligocene transition in the massignano section northern apennines italy abstract the eocene oligocene transition represents the latest greenhouse icehouse shift faced by earth a major global climate change associated with carbon cycle perturbation in this paper we investigate the massignano stratigraphic section northern apennines italy gssp of the eocene oligocene boundary by x ray diffraction analysis of clay minerals and carbon and oxygen stable isotopes to explore the link among climate paleoweathering and runoff and carbon cycle in the neotethys across this major climatic transition we examine the interplay between global climate forcing and orogen evolution controlling the massignano hemipelagic sedimentation the late eocene clay mineral assemblages indicate that the neotethys was sensitive to global eustatic changes as well as changes in composition and rates of weathered sediments accumulating into the basin the carbon isotope record matches with the global signal showing productivity pulses linked to cooling phases and sea level drops before 34 8 ma subsequently a constant negative trend is recorded which is consistent with the global carbon isotope curve and attests for a decrease of primary productivity linked to decreasing atmospheric co2 this negative trend ends at the eocene oligocene boundary when the onset of the global carbon isotope positive excursion is recorded also within the massignano hemipelagic succession on the contrary the clay mineral assemblage is quite constant across the eocene oligocene boundary reflecting the complex interplay among fluvial discharge sea level changes and orogen dynamics which clouded the global climate shift in this context the enhanced fluvial discharge likely contributed to sustain high trophic conditions in the adriatic waters and in turn the oligocene positive carbon isotope shift these results highlight how clay minerals proved to be a useful proxy to identify the interplay between global and regional controlling factors on hemipelagic sedimentation and their integration with the carbon isotope record provides insights into carbon cycle dynamics

sluggish and steady focussed flows through fine grained sediments the methane derived cylindrical concretions of the tertiary piedmont basin nw italy abstract in the cenozoic succession of the tertiary piedmont basin nw italy a wide array of methane derived carbonate rocks including both seafloor and sub seafloor products have been reported in the last decades the most intriguing features are cylindrical concretions more than 1 m long and around 10 cm across that were found within fine grained sediments of messinian age in their original stratigraphic position crossing the bedding planes at high angles these concretions result from cementation of the host muddy sediments by intergranular dolomite microcrystals and lack any evidence of exposure at the sea floor their c and o stable isotope signature suggests that dolomite precipitation was induced by anaerobic oxidation of methane possibly sourced by gas hydrate destabilization such cylindrical morphologies are interpreted as the result of carbonate precipitation and cementation of the sediments around fluid conduits and record a relatively long period of steady sluggish flux of methane rich fluids that opened their way rising up through fine grained unconsolidated sediments they formed immediately below the sea floor in a narrow horizon bracketed between the sulphate methane interface and the oxic anoxic interface cylindrical concretions represent only the highest part of pipes through which methane rich fluids flowed up the deeper part of the conduits conversely left no trace in the stratigraphic record because of the lack of chemical microbiological conditions favourable for carbonate precipitation

paleomagnetic evidence for neogene tectonic rotations in the northern apennines italy abstract paleomagnetic analysis was carried out in the northern apennines on eocene to pliocene epiligurian units five early miocene and two middle miocene sites yielded dual polarity site mean directions which show signs of clustering after correction for bedding tilt these likely primary magnetizations in conjunction with data from the literature give an overall mean late oligocene middle miocene paleomagnetic pole which shows a large and significant counterclockwise rotation of 52 8 with respect to the africa reference paleopoles or a similar amount of rotation with respect to the coeval europe reference paleopole however this paleopole falls close to the roughly coeval paleopole for corsica sardinia which is here calculated by averaging data from the literature three additional early miocene sites from an area west of parma affected by pliocene tectonics yielded site mean directions which pass the fold test and are rotated counterclockwise by a lesser amount than the rest of the miocene sites most of the remaining sites bear paleomagnetic directions acquired after tilting during a recent phase of remagnetization we suggest that the large scale rotation observed in the northern apennines was associated with the motion of the corsica sardinia block within the general context of the africa europe relative motions a compilation of published data from the central apennines also shows a differential rotation of the northern relative to the southern umbria belt which occurred after the motion of corsica sardinia and may have been due to pivoting of the northern umbria belt against a deep seated lineament during the non rotational opening of the tyrrhenian sea

high resolution radar mapping of internal layers at the north greenland ice core project existing accumulation maps with reported errors of about 20 are determined from sparsely distributed ice cores and pits a more accurate accumulation rate might be obtained by generating continuous profiles of dated layers from high resolution radar mapping of near surface internal layers in the ice sheet isochrones to generate such profiles we designed and developed an ultrawideband radar for high resolution mapping of internal layers in the top 200 m of ice and tested it at the north greenland ice core project drill site reflection profiles of 2 and 10 km length reveal horizons that we correlate with electrical conductivity measurement ecm recordings our results show that the radar determined depth of internal layers is within 2 m of that in an ice core collected at a nearby location preliminary frequency analyses of layer reflections reveal that the reflections are strongest at the 500 1000 mhz frequency range long term accumulation rate computed from radar data is within 5 of that obtained from snow pits

polyphasic carbonate precipitation in the shallow subsurface insights from microbially formed authigenic carbonate beds in upper miocene sediments of the tertiary piedmont basin nw italy article i nfo authigenic methane derived carbonates hosted in upper miocene slope sediments of the tertiary piedmont basin nw italy are studied by a multidisciplinary approach including petrography stable oxygen and car bon isotopes of carbonates as well as lipid biomarkers in order to explore the relationship between microbial activity and carbonate precipitation in the shallow subsurface the studied rocks show a bed parallel geom etry and are characterized by dolomitic intergranular cement which is typified by positive 13 c values as high as 6 2 vpdb a striking feature of some dolomite beds is an intricate network of septarian like cracks filled with both injected sediments and polyphasic carbonate cements prokaryotic molecular fossils in the dolomite beds comprise archaeol 13 c 40 vpdb and various bacterial dialkyl glycerol diethers dages 13 c 30 vpdb strongly suggesting that dolomite precipitation took place at the interface of the zones of archaeal methanogenesis and bacterial sulphate reduction in contrast extremely negative 13 c values of carbonate cements as low as 56 3 vpdb and various archaeal and bacterial molecular fossils e g pentamethylicosane pmi 106 vpdb are recorded in the crack filling carbonate cements these cements precipitated due to anaerobic oxidation of methane coupled to sulphate reduction we pro pose a scenario for the formation of the diagenetic beds suggesting that carbonate precipitation was the re sult of three microbially driven processes sulphate reduction methanogenesis and finally anaerobic oxidation of methane this unusual sequence was a consequence of a dynamic change of environmental geo chemical conditions and fluid circulation patterns that prevailed in the ancient subseafloor during early dia genesis of the unconsolidated sediments anaerobic oxidation of methane which usually predates methanogenesis during increasing burial postdates methanogenesis in case of the septarian like beds after the beds were affected by crack formation induced by overcritical pore pressure allowing the ingress of sulphate rich water from above and methane rich water from below

hydrocarbon seepage during the messinian salinity crisis in the tertiary piedmont basin nw italy abstract seep carbonate deposits of messinian age have been recently found in the tertiary piedmont basin nw italy these carbonates are preserved as blocks within a chaotic unit emplaced during the messinian salinity crisis msc they show negative 13 c values from 27 to 15 vpdb that indicate the involvement of hydrocarbon rich fluids in their genesis three types of carbonates are recognised i vuggy carbonates ii lucina carbonates and iii tubeworm carbonates vuggy carbonates are characterised by carbonate pseudomorphs after gypsum and probably formed during the first stage of the msc they are the product of a complex diagenesis influenced by both hypersalinity and seepage of hydrocarbon rich fluids these rocks lack chemosymbiotic assemblages reflecting their formation under extreme environmental conditions inhospitable for most metazoans in contrast lucina and tubeworm carbonates are characterised by chemosymbiotic macrofauna represented respectively by lucina bivalves and putative vestimentiferan tubeworms the latter have not commonly been documented in ancient seep carbonates and have never been reported from the messinian sediments of the piedmont basin both lucina and tubeworm carbonates are interpreted as the product of hydrocarbon seepage during the second msc stage these two types of carbonates formed under less severe conditions than the vuggy carbonates allowing the survival of seep dwelling metazoans during the second msc stage the seafloor was probably characterised by an irregular topography and a thin bottom layer of dense anoxic brines produced by the dissolution of gypsum it is suggested that vestimentiferan worms were able to thrive on morphologic highs with the posterior part of tubes just below the oxic anoxic interface but the anterior part projecting into oxic water the infaunal lucina bivalves were only able to live at seeps with an overlying oxic water column the studied carbonate deposits show features reflecting the uncommon interaction of hydrocarbon rich seep fluids and sulphate enriched waters the latter resulting from both evaporation and dissolution of gypsum and allow to reconstruct the evolution of a seepage system during the msc

origin of mud in turbidites and hybrid event beds insight from ponded mudstone caps of the castagnola turbidite system north west italy the partitioning of different grain size classes in gravity flow deposits is one of the key characteristics used to infer depositional processes turbidites have relatively clean sandstones with most of their clay deposited as part of a mudstone cap or as a distal mudstone layer whereas sand bearing debrites commonly comprise mixtures of sand grains and interstitial clay hybrid event beds develop alternations of clean and dirty clay rich sandstones in varying proportions analysis of co genetic mudstone caps in terms of thickness and composition is a novel approach that can provide new insight into gravity flow depositional processes bed thickness data from the ponded castagnola system show that turbidites contain more clay overall than do hybrid event beds the castagnola system is characterized by deposits of two very different petrographic types thanks to this duality analyses of sandstone and mudstones composition allow inference of which proportion of the clay in each of the deposit types was acquired en route in combination with standard sedimentological observations the new data allow insight into the likely characteristics of their parent flows clean turbidites were deposited by lower concentration long duration erosive muddy turbidity currents which were more efficient at fractionating clay particles away from their basal layer hybrid event beds were deposited by shorter duration higher concentration less erosive sandier flows which were less efficient at clay fractionation the results are consistent with data from other turbidite systems for example marnoso arenacea the approach represents a new method to infer the controls on the degree of clay partitioning in gravity flow deposits

new data for the kinematic interpretation of the alps apennines junction northwestern italy alps and apennines are juxtaposed within an approximately 100 km wide area covered by the upper eocene to miocene successions of the tertiary piedmont basin the upper eocene oligocene evolution of this area was characterized to the north and west by the propagation of the se verging southalpine thrust fold belt that can be traced from the po plain subsurface until the torino hill saluzzese area and to the south by a high angle broadly e w oriented megashear zone that led to the juxtaposition of different crustal levels and controlled the development of a mosaic of partly independent sub basins since the latest oligocene the n verging apenninic tectonics prevailed in the collisional system and the tertiary piedmont basin evolved as a wide thrust top basin bounded to the north by the n verging monferrato arc and characterized by a tectono sedimentary evolution recording changes of subsidence and shift of depocentres in relation to crustal structures

structural anatomy of the ligurian accretionary wedge monferrato nw italy and evolution of superposed melanges we document in this study the internal structure of the late cretaceous late oligocene ligurian accretionary wedge in northwestern italy and the occurrence in this exhumed wedge of broken formation and three different types of melanges that formed sequentially through time the broken formation is the oldest unit in the accretionary wedge and shows bedding parallel boudinage structures which developed as a result of layer parallel extension at the toe of the internal part of the alpine wedge front during the late cretaceous middle eocene this broken formation experienced an overprint of tectonic diapiric and sedimentary processes as a result of continental collision in the late oligocene the ne vergent thrusting and associated shortening produced a structurally ordered block in matrix fabric through mixing of both native and exotic blocks forming the tectonic melange the concentration of overpressurized fluids along the thrust fault planes triggered the upward rise of shaly material producing the diapiric melange which in turn provided the source material for the downslope emplacement of the youngest late oligocene sedimentary melange the sedimentary melange units unconformably cover the collisional thrust faults constraining the timing of both this episode of contractional deformation related to continental collision and the combination and overlap of tectonic diapiric and sedimentary processes our multiscale structural analysis of the ligurian accretionary wedge shows that tectonic diapiric and sedimentary processes played a significant role in its evolution and that the interplay between and the superposition of these different processes strongly controlled the dynamic equilibrium of the accretionary wedge in the nw apennines western alps this kind of polygenetic melange development may be common in many modern and ancient accretionary complexes and the processes involved in their formation are likely to be responsible for major tsunamic events in convergent margins

radar internal layers from the greenland summit ice penetrating radar measurements made over the summit region of greenland show returns from internal layers which can be used to augment the interpretation of climate information from the two deep cores recently recovered from this area these reflecting surfaces believed to represent isochrones give information about the stress regime near the summit and may aid in a better calibration of the age depth scale between the two cores particularly in the lowest 10 of ice thickness where there is currently disagreement the approximate depth at which internal echoes become discontinuous corresponds with the observations of steep inclinations and overturned folds on the scale of centimeters in the core samples however the deepest internal layers which can be distinguished in the profiles place constraints on the scale and location of high angle or overturned folds

tertiary structural relationships between alps and apennines the critical torino hill and monferrato area northwestern italy the relationship between the alpine and apenninic orogenic systems is concealed at the surface by tertiary sediments of two main tectono stratigraphic units the alpine related torino hill domain and the apennines related monferrato domain mapping and structural analyses carried out in the area behind the mio pliocene apenninic padane thrust front allow comparison of the kinematic history of the torino hill and monferrato domains these are separate by the transpressive tlio freddo deformation zone rfdz interpreted here as the superficial expression of a crustal discontinuity along which the alpine metamorphic basement overrode the apenninic ligurian nappes during the palaeogene the western monferrato structural setting is the result of i late oligocene burdigalian transpressive tectonics due to lateral displacement between the alps related and the apennines related domains and ii compressive post messinian tectonics related to northward transport along the main padane thrust front post messinian tectonic events affected also the nw vergent asymmetrical torino hill anticline

paleoenvironmental change in a precession paced succession across the onset of the messinian salinity crisis insight from element geochemistry and molecular fossils abstract in marginal mediterranean sub basins the early phase of the messinian salinity crisis msc is recorded by cyclic successions of gypsum and shales which in deeper parts of the sub basins make lateral transition into organic rich shales marls and carbonates the cyclic stacking pattern of the gypsum bearing sequences is assumed to reflect periodic paleoenvironmental change induced by precession driven climate perturbations with the assumption that shales reflect humid climate precession minima while gypsum reflects arid conditions precession maxima however this correlation has not been verified to date mostly because of the scarcity of microfossils the most commonly used tools for the reconstruction of precession driven paleoenvironmental change such change can instead be reconstructed through the study of the deeper water counterparts of gypsum marly and carbonate layers with geochemical indicators major and trace elements molecular fossils which provide insight on climate and aquatic productivity we used this approach to study a section from the piedmont basin nw italy where the onset of the msc is archived in a sequence of organic rich sediments this sequence displays distinct lithological cyclicity evidenced by the repetition of couplets of organic rich shales and marls either bioturbated in the pre msc part of the section or laminated during the msc the influence of orbitally driven precession climate oscillations is demonstrated by fluctuations of ti al si al mg al k al zr al and ba al ratios that are in phase with lithological cyclicity these fluctuations are interpreted to reflect alternation of humid shales deposited during precession minima and arid bioturbated and laminated marls deposited during precession maxima phases dominated by fluvial and aeolian transport of detrital material respectively the cyclicity of the element ratios is mirrored by changes in organic carbon content and molecular fossil inventory in particular the distribution of long chain n alkanes and their degree of preservation reveal that humid phases at times of precession minima were typified by the maximum input of degraded terrestrial organic matter driven by enhanced riverine runoff which promoted water column stratification coeval increase in ba content a common paleoproductivity proxy agrees with enhanced nutrient supply during humid periods promoting phases of eutrophication in the basin lithological and geochemical changes are observed in msc sediments deposited at times of precession maxima evidenced by the replacement of pre msc bioturbated marls by laminated marls rich in filamentous fossils corresponding to the remains of probable colorless sulfide oxidizing bacteria such changes reflect an intensification of water column stratification after the onset of the msc possibly related to the combined effect of persistent freshwater inflow and basin isolation preluding the advent of gypsum precipitation

influence of structural inheritance on foreland foredeep system evolution an example from the po valley region northern italy understanding the development of foreland foredeep systems and the influence exerted by pre existing structures on their evolution is an important step for defining the key factors that control long term basin and lithosphere dynamics comprehending the associated seismic hazard and assessing their economic potential in the domain of hydrocarbon exploration the po valley is a rather unique foreland basin for two major reasons a it developed intermittently at the front of two different mountain chains the northern apennines and the southern alps progressively converging one towards the other b the inherited structures mainly derived from the mesozoic extensional tectonics are oriented at high angle to the advancing belts the coexistence of these two factors and their various implications make the po valley basin a complex case study that deserves attention taking advantage of the recent building of a 3d structural model across the region we reconstructed the possible geometry and migration pattern of the tertiary basins that developed at the front of the northern apennines and the southern alps as part of the po valley tectonic evolution in addition a number of sections sliced from the 3d model across selected domains have then been used to restore the present day structural units to their pre compressional setting while highlighting the key stages of their geological history results from the model analysis show that the mesozoic extension related tectonics and the associated carbonate facies geometry and distribution localized and constrained the alpine structures inside around the basin their control on the cenozoic deformation and sedimentation is evident during the paleogene and the miocene whereas it becomes more subtle during the plio pleistocene when lithospheric scale mechanisms need to be invoked notwithstanding the model uncertainties and its explicit regional significance our results may be taken as reference for any foreland foredeep setting worldwide especially in complex systems where tectono sedimentary inhomogeneity is spatially and temporally dominant

the role of pre existing faults in the structural evolution of thrust systems insights from the ligurian alps italy abstract new structural and stratigraphic data for a selected area of the ligurian alps are combined in order to assess and discuss the role played by extensional structures in the southernmost segment of the western alps during thrusting restored cross sections and field data suggest that the structural style in the external sector of the chain may depend upon the presence of pre orogenic normal faults ascribed to three extensional events linked to different geodynamic contexts i permian post variscan plate reorganisation ii mesozoic rifting drifting phases leading to the opening of the alpine tethys and iii eocenic development of the european foreland basins during positive inversion in eocene times a thin skinned thrust system developed in this area followed by a thick skinned phase in both situations the inherited extensional structures played fundamental roles during the thin skinned phase they conditioned the thrusting sequence also producing large scale buckle folds and partial reactivations during the thick skinned phase the strain was compartmentalized and partitioned by pre existing faults the kinematic model of the external sectors of the ligurian chain also allows the re assessment of the alpine evolution of the front foreland transition including i indirect confirmation that in the eocene the ligurian brianconnais and dauphinois domains were not separated by the valais pyrenean oceanic basin ii that the thin skinned phase progressively changed into thick skinned iii the assertion that there were no significant deformations from the oligocene to the present day and the corsica sardinia block rotation only produced a change in orientation of previously formed structures and normal fault system development

flocculent layers and bacterial mats in the mudstone interbeds of the primary lower gypsum unit tertiary piedmont basin nw italy archives of palaeoenvironmental changes during the messinian salinity crisis abstract the recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the messinian late miocene primary lower gypsum unit 5 97 5 60 ma of the piedmont basin nw italy provides information on the palaeoenvironmental evolution at precessional insolation maxima these cyclic layers consist of irregular alternation of cm thick grey terrigenous laminae and whitish composite packets the latter is in turn composed of sub mm thick wrinkled dolomite rich laminae that alternate with terrigenous ones two types of layers can be distinguished i peloidal layers composed of faecal pellets and irregular diatom rich aggregates interpreted as marine snow floccules and ii filament bearing layers composed of interwoven filaments up to 150 m across corresponding to remains of beggiatoa like giant sulphide oxidising bacteria by comparison with present day settings the peloidal layers are interpreted as flocculent layers deposited on anoxic sea bottoms following episodes of phytoplankton bloom in the upper water column the filament bearing layers are considered as chemotrophic microbial mats growing on dysaerobic sea bottoms the uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface induced by bacterial sulphate reduction the laminated layers are the first reported example of a high frequency climate driven cyclicity in the non evaporitic portion of the primary lower gypsum unit their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle culminating with gypsum deposition at the onset of the arid phase

polarization of radio waves transmitted through antarctic ice shelves the polarization behaviour of radar waves transmitted through two antarctic ice shelves has been investigated using a step frequency radar with a centre frequency of 300 mhz and a bandwidth of 150 mhz one site was on brunt ice shelf at a site near halley station and 17 sites were oil george vi ice shelf near the southern ice front birefringence in the ice dominated the behaviour oil brunt ice shelf where the anisotropy in the effective permittivity was found to be about 0 14 on george vi ice shelf a highly anisotropic reflecting surface was the controlling feature suggesting a fluted ice shelf base formed by oceanographic currents

radio wave depolarization and scattering within ice sheets a matrix based model to link radar and ice core measurements and its application crystal orientation fabric cof has a large influence on ice sheet flow earlier radar studies have shown that cof based birefringence occurs within ice sheets radio wave scattering in polar ice results from changing physical properties of permittivity and conductivity that arise from differing values of density acidity and cof we present an improved mathematical model that can handle all these phenomena together we use this matrix based model to study the two way propagation of depolarized radio waves that scatter at both isotropic and anisotropic boundaries based on numerical simulations we demonstrate how cof affects the radar signals in terms of radar polarization and frequency we then compare the simulated features with vhf radar data obtained at two contrasting inland sites in east antarctica where cof is known from ice core studies these two sites are dome fuji located near a dome summit and mizuho located in a converging ice flow region data at dome fuji are dominated by typical features resulting from birefringence in contrast both birefringence and anisotropic scattering affect the radar data at mizuho we argue that radar methods can be used to determine principal axes and strength of birefringence in the ice sheets

outcrop and seismic expression of stratigraphic patterns driven by accommodation and sediment supply turnarounds implications on the meaning and variability of unconformities in syn orogenic basins abstract tectonically complex settings present accommodation and sediment supply changes with patterns and rates for which the current sequence stratigraphy paradigms are not designed in the tertiary piedmont basin tpb and peri adriatic basin pab outcrop and seismic examples demonstrate that the observed stratal and stacking patterns cannot be entirely explained using conventional sequence stratigraphic models therefore it is of paramount importance to use a model independent more comprehensive approach encompassing advanced sequence stratigraphic concepts combined with process changes while being able to consider the morphostructural complexity that characterizes these margins and their changes induced by basin reshaping abrupt relative sea level falls generated by uplift or basin inversion may exceed several hundreds of meters resulting in wedge margin progressive unconformities characterized by subaerial and subaqueous erosional truncation a progressive increase in sediment supply occurs expressed by increasing volume and size of mass transport complexes overlain by forced regressive deltas as the maximum sediment supply is delayed until after the main uplift different accommodation sediment supply ratios may also occur at the same time along different margins of the same basin generating a diachronism in the t r or r t cycles adding further complexity to the variability produced by autogenesis on clastic shelf margins characterized by an increasing rate of relative sea level rise such as in case of increasing rollback velocities and related flexural tilting or following an orogenic collapse sediment supply may not keep pace with increasing accommodation so that initially retrogradation and basinward condensation occur marked by omission surfaces however when the rate of subsidence increases the succession is punctuated by multiple subaqueous erosional unconformities marking phases of basinward tilting leading to the oversteepening of basin margins and abrupt deepening the downwarping usually produces large scale subaqueous erosional surfaces passing laterally into paraconformities so hinged margin drowning unconformities affecting clastic shelves occur associated with regional stratigraphic gaps the re establishment of the slope equilibrium profile implies high volume of sediments eroded from drowned deltas and shelves feeding turbidites deposited at the toe of above grade slopes these turbidites can be therefore considered as high accommodation high sediment supply systems this suggests that turbidites are delivered basinward not only due to bypass at sequence boundaries or during the highstand progradation of supply driven deltas but also due to abrupt accommodation creation on hinged shelf margin wedges the great variability of tectonically driven unconformities generated under either decreasing or increasing accommodation suggests that the features described in the tpb and the pab are probably not uncommon controlled by linked dynamic turnarounds of accommodation sediment supply and stratigraphy taking place throughout the development of basin reorganizations

the response of water column and sedimentary environments to the advent of the messinian salinity crisis insights from an onshore deep water section govone nw italy

the parona chaotic complex a puzzling record of the messinian late miocene events in monferrato nw italy the parona chaotic complex pcc from monferrato nw italy is a melange composed of carbonate cemented blocks floating in a matrix of weakly consolidated mud breccias it forms a minor 1 km2 chaotic sedimentary body enclosed in a larger messinian melange that rests unconformably on older deposits and is followed again unconformably by pliocene sediments three main facies have been recognized in the blocks a bioclastic rudstones and coquinoid grainstones of early messinian age composed of oligotypic assemblages of gastropods and the brackish water bivalve cerastoderma mixed with shallow water marine biota mollusks corallinae algae benthic foraminifers echinoid fragments rare ahermatypic corals these sediments record shallow water carbonate sedimentation with episodic brackish incursions and show a peculiar diagenetic overprint selective dissolution of aragonitic grains and early dolomitic cements b monogenic breccias composed of clasts of coquinoid grainstones floating in a dolomitic microcrystalline matrix c polygenic conglomerates composed of rounded clasts of pre messinian pelagic sediments of lower messinian bioclastic carbonates and of messinian evaporitic carbonates finally a few blocks of strongly cemented micritic limestones interpreted as methane derived carbonates for the geochemical signature of the carbonate phases strongly depleted in 13c are present the matrix enclosing the blocks is a mud breccia containing centimeter sized clasts of marly sediments micropaleontological analyses have shown that lower messinian and upper tortonian planktic foraminifers are mixed with lower miocene oligocene and eocene forms the pcc results from complex processes involving 1 deposition of the peculiar sediments preserved in the blocks and 2 their dismemberment and mixing as for the depositional history composition of the blocks has allowed to sketch the following evolution a deposition of bioclastic rudstones and coquinoid grainstones that are interpreted as lower messinian carbonate platform deposits for their strong compositional and diagenetical similarity with the lower messinian carbonates cropping out in the mediterranean region the monferrato bioclastic sediments are the northernmost example of messinian shallow water carbonates yet known b deposition of monogenic breccias they formed during the evaporitic phase of the messinian that was accompanied by a relative sea level drop and by erosion of the previously deposited coquinas depositional and diagenetical processes during the evaporitic phase are also recorded by clasts of evaporitic carbonates in the polygenic conglomerates c deposition of polygenic conglomerates that are interpreted as upper messinian post evaporitic fan delta facies resulting from an important erosional phase after deposition this succession was dismembered in the blocks forming the present day melange geometry stratigraphic relationships and internal characteristics of the pcc point to an origin related to gravity driven phenomena triggered by tectonics however the faunal mixing in the mud breccias and the occurrence of blocks of methane derived carbonates suggest that mud diapirism also played a role for the genesis of the pcc this latter mechanism which has been poorly considered until now could also have been effective in the genesis of messinian chaotic deposits that extensively crop out in nw italy

crystalline texture of the 2083 m ice core at vostok station antarctica crystalline texture and c axis orien tation of the 2083 m ice core at vostok station covering more than 150 kyear reveal the existence of strong anisotropies changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries a smaller growth rate appears to be associated with cold periods a gradual increase in the horizontal elongation of grains was observed between 350 and 680 m but the mean value of the coefficient of the linear dimensional orientation of grains does not cha nge below 700 m the e axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains forming a vertical girdle patt ern this charac teristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longit udi nal tension the rotation of grains was calcu lated with respect to the total strain simulating the form ation of the girdle fabric pattern the fabric enhance ment factor was calculated at various depths it appears that vostok ice hardens gradua lly