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The magnetic fabric and grain size of sand deposits emplaced during the 2011 Tohoku-oki tsunami were studied in five trenches along a 1800 m long shore normal transect on the Sendai plain as well as in a near shore sedimentary infill of a scour depression. The magnetic susceptibility in all deposits is due to ferromagnetic minerals (mainly magnetite) making the anisotropy of magnetic susceptibility (magnetic fabric) suitable for fabric analyses. The dominant magnetic fabric is planar in all trenches and stronger in finer-grained inland deposits than in the coarser sediments. This planar fabric is related to tractive shearing of the bedload basal portion of the tsunami flow that led to the deposition of traction carpet layers. Among the various fabric parameters used for this study, the vertical evolution of the shape factor ( q ) of the magnetic ellipsoid in each trench follows the evolution of the magnetic lineation ( L ) and foliation ( F ). These parameters provide information on the hydrodynamic energy (flow speed) fluctuations during the emplacement of the tsunami deposit. For the most proximal deposits, characterized by well-sorted reworked beach sand with minor fluctuations in grain-size distribution, the magnetic fabric is sensitive to hydrodynamic energy variations during sedimentation. Reconstruction of tsunami flow orientation in the sediments, based on the orientation of the mean K max calculated for each trench, appears to be unambiguous only for the sandy infills of small topographic depressions. The variations in flow direction indicators elsewhere could be related to local variation of the flow and to micro-topographic effects. These findings are encouraging for the use of the magnetic fabric proxy in the study of paleotsunami deposits.

A multi-proxy approach using trench sediment analysis on the southwestern coast of Spain (Los Lances Bay, Andalusia) provides a high-resolution record of the 1755 Lisbon tsunami and offers new means to interpret tsunami deposits. A combination of sedimentological (grain size, sorting, AMS), micromorphological (X-ray tomography and radiography, thin sections) and geochemical analyses (X-ray microfluorescence, ICP-AES) combines to provide a comprehensive reconstruction of the different phases of tsunami deposition and flow dynamics. Vertical variations in sediment texture, fabric and composition of the 1755 tsunami deposits in Los Lances are then discussed with reference to existing literature on diagnostic criteria commonly used for identifying and interpreting tsunami deposits. Finally possible leads for future investigation are proposed.

article i nfo Some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, and a revised toolkit provided. The new application of anisotropy of magnetic susceptibility (AMS) to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences, together with data from grain size analysis, are presented. The value of chemical proxies as indicators of saltwater inundation, associated marine shell and/or coral, high-energy depositional environment, and possible contamination, is demonstrated and issues of preservation addressed. We also provide new findings from detailed studies of heavy minerals. New information gathered during the UNESCO — International Oceanographic Commission (IOC) International Tsunami Survey of fine onshore sediments following the 2009 South Pacific Tsunami is presented, and includes grain size, chemical, diatom and foraminifera data. The tsunami deposit varied, ranging from fining-upward sand layers to thin sand layers overlain by a thick layer of organic debris and/or a mud cap. Grain size characteristics, chemical data and microfossil assemblages provide evidence for marine inundation from near shore, and changes in flow dynamics during the tsunami.

International audience; The Lauzanier area represents the northernmost extension of the Annot Sandstone series and contains deposits between 650 and 900 m-thick. This basin was active from upper Bartonian or lower Priabonian to early Rupelian. It is composed of two superposed units separated by a major unconformity. The sediment supply is due to channelled flows coming from the south. Flow processes include mass flow to turbidity currents. The size of the particles and the absence of fine-grained sediment suggest a transport over a short distance. The Lower Unit is made of coarse-grained tabular beds interpreted as non-channelled lobe deposits. The Upper Unit is made of massive conglomerates interpreted as the channelled part of lobes. These lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale. The abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area. This uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts. This field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse-grained turbidite system. The outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non-channelled lobe system. These results of high-resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep-sea turbidite system that are either restricted to cores, or with a lesser resolution (seismic).

article The main sediment depocenter along the Oman margin is the Al Batha turbidite system that develops in the Gulf of Oman basin. It is directly connected to the wadi Al Batha, and forms a typical sand and mud rich point source system that acts as regional sediment conduit and feeds a ~1000 km 2 sandy lobe. The Al Batha lobe depositional architecture has been investigated in detail using very high-resolution seismic, multibeam echosounder data and sediment cores. Several scales of depositional architecture can be observed. The Al Batha lobe is composed of several depositional units, made of stacked elementary sediment bodies (thinner than 5 m) that are each related to a single flow event. The lobe is connected to the feeder system through a channel-lobe transition zone (CLTZ) that extends on more than 25 km. The lobe can be divided into proximal, middle and distal lobe areas. The proximal lobe is an area of erosion and by-pass with small axial feeder channels that rapidly splay into several small distributaries. They disappear in the mid-lobe area where deposits consist of vertically stacked tabular to lens-shaped sediment bodies, with a lateral continuity that can exceed 10 km. The distal lobe fringe shows a classical facies transition towards thin- bedded basin plain deposits. Sub-surface deposits consist of sandy turbidites and hyperpycnites, interbedded with fine-grained deposits (thin turbidites, hyperpycnites, or hemipelagites). Although these distal deposits are mainly related to flow transformations and concentration evolution, they highlight the importance of flooding of the wadi Al Batha on the sediment transfer to the deep basin. The thick sandy hyperpycnites recovered in such a distal area are also possibly related to the initial properties of gravity flows, in relation to the flooding characteristics of mountainous desert streams.

The transformations of volcaniclastic gravity flows entering the sea remain poorly understood. They are recorded by sedimentary signatures in the volcaniclastic sedimentation of the Mio–Pliocene Las Palmas Detritic Formation (LPDF) of the volcanic island of Gran Canaria. These gravity flows are contemporaneous with an erosive period on the island succeeding the emplacement of the Fataga Volcanic Group, and the beginning of the evolution of the Roque Nublo stratovolcano. The sedimentary section that crops out at the mouth of a paleobarranco at Las Cuevas del Guincho comprises subtidal calcareous and clastic sediments affected by wave and storm action (Units 1 and 3), beach gravels (Unit 4), volcaniclastic deposits represented by reworked phonolitic pyroclastic deposits (Unit 1), breccia deposits that contain juvenile and phonolitic gravels and blocks mainly incorporated at the shoreline (Unit 2), and a debris avalanche deposit at the top (Unit 5). The breccia deposits display a reversely graded base which disappears distally as a result of seawater incorporation and liquidization of the volcaniclastic mass and mixing with marine sediment. This breccia unit is interpreted as having been emplaced by a granular mass flow after transformation of a block and ash flow deposit that entered the sea. In the debris avalanche deposits, thermal quenching of juvenile basaltic lava clasts and large inclined clastic intrusions of underlying marine sediments suggest that the debris avalanche entered the sea. Rapid subaqueous emplacement of the granular mass flow and of the debris avalanche deformed the sedimentary substratum. Water incorporation reduced the influence of the volcaniclastic flows on the substratum. AMS data confirm the effect of water ingestion and correlative loss of cohesion and allow also reconstruction of paleoflow directions that were normal to the paleoshoreline of the northern coast of Gran Canaria. All these volcaniclastic gravity flow deposits and their textural characteristics are particularly useful in the reconstruction of processes that occur at the subaerial–submarine transition and for the location of ancient shorelines.

The Holocene sturzstrom of Flims, Grisons, Switzerland mobilized 12 km3 of Jurassic limestone making it one of the largest events of this kind on the earth. The material dammed a 10-km-long reach of the upper Rhine River Valley with thicknesses up to 400 m. A 40-km-long natural lake was formed upstream. The body of the avalanche deposits displays a well-preserved internal fabric. Five major sedimentary facies were identified related to the confinement of the deposits in a narrow valley that restricts the spreading of transported material. In the deepest parts of the avalanche deposit, a stratified facies attests that the movement was mainly non-turbulent, whereas a granular facies appears in the lateral and upper parts. The relative position of these facies within the natural dam has played an important role in the way the water flow eroded the dam crest and emptied the lake as suggested by the present valley slope morphology. Ledges corresponding to the levels of the different facies on north and south slopes of the valley correspond to steps in the narrowing of the incision. The outburst of the dam, if it occurred, only affected the upper part of the deposits that corresponds to the poorly cohesive granular facies. One hundred kilometres downstream, in Lake Konstanz (Bodensee) lacustrine sediments, the presence of two layers, contrasting with the normal grey varved deposits and separated by six laminites, are contemporaneous with the mass movement. These layers, which could correspond to the outburst of the dam, point to not one, but two major overflooding events.

A sturzstrom is a large-scale landslide that evolves during transport into a rapid granular flow (rock avalanche) by a dynamic disintegration process. Numerous theoretical hypotheses have been proposed to explain the excessive mobility of these catastrophic mass movements, but the role of disintegration processes remains poorly understood. Exceptional outcrop conditions at the giant (12 km3) Flims sturzstrom (Swiss Alps) permit the analysis of disintegration processes that result from shearing during transport. In confined zones of the rock mass, shearing is concentrated along preferred surfaces (originating as bedding planes), which evolve into shear band layers. Differential velocities of slabs separated by these shear layers induce oblique fractures in the slabs by accommodation. Contacts between grains are maintained in the shear layers. In unconfined zones near the top and the lateral margins, shearing generates dilatancy. The rock mass is affected by anisotropic dispersion without mixing, and disintegrated material is preferentially produced to the top due to inflation. The rock slide then evolves to a granular flow. The consequence of these processes is the formation of two distinct depositional facies in the sturzstrom. The structured facies exhibits a stratified aspect close to the base, reflecting confined slab-on-slab shearing motion. Towards the top and distally, it evolves into a chaotic facies with some isolated pockets of the structured facies. Reduction of confining forces on the moving sturzstrom allows transformation of the structured facies into the chaotic facies. This characteristic transition, observable in many sturzstrom deposits, seems to be necessary for the rock avalanche process to occur, and offers insights into the long-runout characteristics of these catastrophic mass movements.

International audience; Miocene marine volcaniclastic deposits occur in Mahia Peninsula (North Island, New Zealand) and were sedimented in a forearc setting related to the Hikurangi trench subduction system. These deposits are interbedded with hemipelagic marls, and correspond to simple or amalgamated centimetric- to metric-thick turbiditic sequences. Volcaniclastic material is mainly composed of vitric particles, with crystals (quartz, plagioclase with minor biotite, amphibole, pyroxene and oxides), which are well represented in the coarse-grained fraction. The glass shards are mainly rhyolitic in composition. Three types of volcaniclastic turbidites were distinguished with geochemical data, because distinction is impossible on sedimentary characteristics. (1) Primary monomagmatic turbidites contain both magmatic (bubble wall pumice and shards) and phreatomagmatic (blocky shards with few vesicles and hydroclastically fragmented pyroclasts) vitric particles. The chemical compositions of the vitric particles and the crystals are very homogeneous suggesting a cogenetic origin. These turbidites directly result from unique eruptive events and are probably related to the entrance of hot subaerial pyroclastic flows into the sea, which also led to their transformation into subaqueous gravity flows. (2) Secondary monomagmatic turbidites never contain phreatomagmatic pyroclasts and the glass compositions display a trend from andesites to rhyolites. There is a strong linear correlation in the compositions that suggest that the glass particles are derived from the same magma. Crystals also show a compositional homogeneity. These deposits reflect the succession of several eruptions related to a unique magmatic system and result of the reworking of volcaniclastic material after relatively short storage on the shelf. (3) Secondary multimagmatic turbidites do not display compositional homogeneity of their vitric and mineral components. This implies that the volcaniclastic material has been stored during a relative long period on the shelf before remobilization, and that this sedimentation records the volcanic activity of multiple magmatic sources. Consequently, it has been possible to distinguish primary volcaniclastic turbidites that are directly related to the volcanic activity, from secondary turbidites that result from reworking of previously deposited material on the shelf. Monomagmatic turbidites can be used as stratigraphic and magmatic markers whereas multimagmatic cannot. Multimagmatic turbidites, however, record the evolution of the volcanic arc during longer periods. This leads to the conclusion that the Mahia Peninsula volcaniclastic turbidites distally record the evolution of the source volcanic arc.

The Sydra Formation is a widespread interglacial complex in the North Volcanic Zone, Iceland, from the sector of the Askja volcano down to Oxarfjordur at the north coast. It probably corresponds to OIS 5e, 5d and 5c. Subsequently, the region was covered by the Weichselian ice cap. It is significant as well for the understanding of the OIS 6 deglaciation and its relations to volcanism as also for the erosional budget of the Saalian, warm based and Weichselian, cold based, glaciations. A topographic bulge linked with a rapid glacio-isostatic rebound, downstream of the Jokulsa a Fjolum river, is responsible for the development of the Sydra lacustrine deposits. An early abrupt event (Sy2), the Sydra ash probably corresponds to ash zone B as on the northern Iceland shelf and possibly an abrupt cooling. It presents no similarity with the Fossvogur formation in the Reykjavik district. The meaning of the formation is significant in term of rift activity and of palaeoclimate for OIS 5.

The Flims sturzstrom deposit (Swiss Alps) is the largest in the Alps (12 km3, H/L = 0.13). It consists of stratified breccias that display planar discontinuities that originated during transport. Major sliding surfaces are underlined by frictional gouge. Between these surfaces, the material is fragmented with rotated fault blocks bordered by oblique fractures that show the transport directions. The transport mechanisms of the debris avalanche were dominated by layer-parallel slip movements that favoured the nonturbulent behaviour of the granular material and the reduction of internal friction.

Large volcanic debris avalanche (VDA) deposits of Miocene age occur within the stratigraphic sequence of Cantal stratovolcano (central France). The VDA of Cantal volcano were initiated by sector collapse of a cone of high elevation (up to 4500 m.a.s.l.). Two distinct superimposed VDA deposit units (Breccias I and II) resulted from at least two successive large-scale collapse events during the evolution of the volcanic complex. Breccia I, the oldest one, is very thick (up to 200 m) and heterolithologic. It is overlain by Breccia II, which is thinner (up to 50 m) and contains more heterometric clasts ranging from hectometer- to millimeter-size. The VDA deposits are poorly sorted. Clasts are angular and highly fractured at different scales, often with jigsaw fit. In Breccia II, jigsaw megaclasts have usually subspheric shapes with size decreasing distally. Basal deposits commonly display thin inversely graded layers, reorientated clasts along ramp structures, and cataclasis of the substratum. Some units have a distal fabric in the form of a poorly developed clast imbrication. The clasts are commonly sub-rounded thereby indicating abrasion during viscous flow. Anisotropy of magnetic susceptibility (A.M.S.) measurements indicate absence of a preferentially oriented matrix fabric. Magnetic foliation parallel to the bedding suggests that the depositional process is dominated by particle settling. The magnetic fabric is better organized in distal deposits where magnetic carriers are imbricated. Moreover, the fragmented clasts and megaclasts are not abraded, rather inflation led to isotropic spherical dispersion of clastic material (=Isotropic Dispersive Inflation) which fed the interclast matrix. This is also confirmed by the lack of rotation at the individual crystal level. All these data strongly suggest transport of VDA by liquified non-turbulent granular flows. Distally, imbricated deposits suggest more turbulent flow. Emplacement of the VDA results from progressive upward aggradation of the particles by volume reduction and deflation loss. The non-turbulent liquified stage of the VDA disappears. The VDA behaves as a sliding rigid mass (plug flow) that exerts strong friction on the basement leading to gouge formation.

Permineralized trunks of five different gymnospermous taxa have been collected in the Lower Carboniferous (Visean) of the southern Vosges. Some specimens are comparable to species previously discovered in this area and may be attributed to the genera Pitus and Eristophyton known from localities in Scotland and Silesia. The fifth type corresponds to the progymnosperm Protopitys which is recorded for the first time in the Vosges. Present evidence suggests an important taxonomic diversification of the arborescent gymnospermous element of the Visean vegetation which was similar in contemporaneous volcanic environments in the Vosges and Scotland.

Four sites have been drilled in the submarine volcaniclastic apron of the volcanic island of Gran Canaria during the ODP Leg 157. The volcaniclastic submarine apron reflects the volcanological evolution of the island. The main volcanic phases are recorded in the sedimentation by an important contemporaneous clastic influx on the apron. However, periods of volcanic quiescence are characterized by very weak sedimentation rates. Consequently, it is possible to establish a volcanostratigraphy from the sedimentary record of the apron.

The Southern Vosges host a large volcano-sedimentary basin which contains clastic sediments of Famennian (Late Devonian; ca. 365 Ma) to Late Visean (ca. 340-335 Ma) age. The basin is bordered by an exhumed high-grade basement complex and intruded by several granitoid plutons. A chronology for basin evolution and magmatism was established dating volcanic rocks of the basin as well as cross-cutting granitoid rocks by the U Pb technique applied to zircon and titanite: The basin evolution started with olistolithic deposits and overlying marine shales that have a Famennian fauna (ca. 365 Ma) and contain detrital zircons with an age of 386 Ma. The lowermost rhyolite flows interlayered with the basin sediments and tholeiitic basalts yielded an age of 345 ± 2 Ma. Following a tectonic event at the bottom of the Upper Visean, the rates of sedimentation and volcanism were strongly enhanced, leading to basin emersion, and were concluded by the extrusion of the uppermost ignimbrite (Molkenrain rhyolite) emplaced at 340 ± 2 Ma. The whole volcano-sedimentary association was subsequently intruded by melts of the Ballons and Creˆtes granites as well as by small monzodioritic and dioritic satellite intrusions along the border of the Ballons granite within 3 ± 2 myr (342 ± 1 to 339.5 ± 2.5 Ma). The zircons of most of the volcanic and plutonic rocks investigated contain inherited lead of 0.6 and 2.1 Ga age. The differences in initial Nd isotopic composition of the Ballons and Creˆtes granites can be explained by differential uptake of crustal material during magma genesis. The precise age data prove that magmatism and basin formation in the Southern Vosges were extremely short-lived and coeval to the exhumation of adjacent high-grade gneiss terrains, revealing an episode of extension at the end of the Lower Carboniferous between 345 and 340 Ma (Visean). The tectonic regime in the internal part of the Variscan orogen is that of extension and strike-slip, while convergent tectonics were still ongoing in the external part of the Variscan orogen.