Salt tectonics and crustal tectonics along the Eastern Sardinian margin,Western Tyrrhenian : New insights from the « METYSS » cruise (June 2009)

International audienceThe « METYSS » cruise was carried out in June 2009 onboard the R/V « Téthys II » along the eastern Sardinian and south-eastern Corsican margins, western Tyrrhenian Sea, in order to better constrain the potential links between deformation related to either crustal tectonics or salt tectonics and sediment accumulation, especially during the Messinian and Plio-Quaternary times. We acquired 15 high-resolution seismic reflection profiles (about 1200 km in cumulative length) along the south-eastern Corsican margin, immediately north of the Bonifacio Strait and along the upper and middle parts of the eastern Sardinian margin, from the continental slope to the Cornaglia Terrace. The Tyrrhenian Sea is considered as a Neogene back-arc basin that opened during continental rifting and oceanic spreading related to the eastward migration of the Apennine subduction system from Tortonian to Pliocene times (Jolivet et al., 2006). Rifting of the Tyrrhenian Sea started first along the Eastern Sardinian margin during the Tortonian-Messinian times and therefore the series of that age should be considered as syn-rift sediments (Sartori et al., 2004). The « METYSS » seismic profiles clearly illustrate that this part of the Tyrrhenian was highly segmented during the rifting stage by N-S trending normal faults delineating ridges (e.g., Baronie Ridge) and basins (e.g., Sardinian Basin and Cornaglia Terrace), as previously described for example by Thommeret (1999) and Sartori et al. (2004). The Messinian sedimentary units and especially the « Upper Unit » (UU, Lofi et al., this congress, corresponding to the « Upper Evaporites » in the previous literature) are, without any doubt, of syn-rift age, as they display a fan-shaped stratal geometry. The Mobile Unit (MU, Lofi et al., this congress), i.e. the Messinian halite, is clearly imaged in the study area and its spatial repartition can be outlined. The highly-variable thickness of the confined salt basins could be due to the initial basin geometry (i.e. before the Messinian salinity Crisis) or to the syn-rift character of the deposition. Southeastward of the study area, in the vicinity of the Cornaglia Seamount, salt tectonics appears surprisingly vigorous. More surprisingly, several normal faults seem to have remained active in recent times, if not even at present time. Fault slip has been recorded by bathymetric scarps and associated footwall debris flows interfingered within the Plio-Quaternary sequence, even though the eastern Sardinian margin is usually considered to be passive now. Moreover, some amount of tectonic inversion is visible on some normal faults that show contractional or transpressional components of late slip. In addition, this “post-rift” deformation can be illustrated within the Plio-Quaternary sequence by a regional unconformity. Consequently, numerous mass-transport deposits and channel-levees systems observed in the Plio-Quaternary cover could be partly controlled by tectonic activity. These very preliminary results require further investigations in order to better decipher the role of crustal tectonics and salt tectonics, salt-related structures being very efficient markers to discriminate between the respective contribution of gravity-driven, salt tectonics and deep-seated, crustal tectonics (Gaullier et al., 2010). Finally, we aim to precisely determine the relative vertical movements (tilting, subsidence, magmatism. . . ) and geodynamical history of the different segments of the area since 6 Ma

Structure and evolution of the Demerara Plateau, offshore French Guiana : rifting, tectonic inversion and post-rift tilting at transform-divergent margins intersection

International audienceWe present the structure and evolution of the eastern part of the Demerara plateau, offshore French Guiana, from the analysis of geophysical data collected during GUYAPLAC cruise. This area is located at the intersection of a transform segment and a divergent segment of a continental margin related to the Early Cretaceous opening of the Equatorial Atlantic. The main structures are NNE-SSW to NNW-SSE trending normal faults on the eastern edge of the plateau, and WNW-ESE to NW-SE trending acoustic basement ridges on its northern edge. When replaced in their Albian position, these structures appear to be parallel to the coeval oceanic accretion axis and transform faults, respectively. The most striking structures are related to a post-rift but syn-transform tectonic inversion, producing E-W to WNW-ESE trending folds, sealed by a regional unconformity. This shortening can not be related to ridge push, but is probably related to a plate kinematic change 105 My ago, that modified the deformation in the vicinity of the transform fault. Late post-rift evolution also includes a significant Tertiary oceanward tilt of the edge of the Demerara plateau. The driving mechanism of this late tilt is unclear, but may be related to a lithospheric flexure resulting from the loading of the abyssal plain by the Orinoco and Amazon deep-sea fans

Sand, salt, and models : The legacy of Bruno Vendeville

Acknowledgements We are grateful for the support of numerous colleagues who contributed, either materially or simply with encouragement, to putting together this memorial to our friend Bruno. The important task of reviewing and editing manuscripts was carried out by the co-editors along with Jürgen Adam, Ian Davison, Tim Dooley, Carl Fiduk, Pablo Granado, Geoffroy Mohn, Webster Mohriak, Van Mount, Josep Anton Muñoz, Thierry Nalpas, Fabrizio Storti, Gabor Tari, Lei Wu, and 16 reviewers who chose to remain anonymous. And of course, this volume would not have happened without the hard work and persistence of the many authors and coauthors who contributed their manuscripts. We also thank Lorna Stewart and other staff at the Journal of Structural Geology for their help and guidance, as well as Tim Dooley for supplying original versions of the figures used here.Peer reviewe

Recent and active deformation pattern off the easternmost Algerian margin, Western Mediterranean Sea: New evidence for contractional tectonic reactivation

International audienceWe describe for the first time a set of large active thrusts and folds near the foot of the easternmost Algerian margin, Western Mediterranean, from swath bathymetry and high-resolution seismic data acquired in 2005 during the Maradja2/Samra cruise. This active system resumes a previous passive margin and creates growth strata deposition on the limbs of large folds, resulting in the development of perched basins at the foot of the margin since less than ~ 1 Ma. They form a set of overlapping fault segments verging toward the Algerian basin, in a way similar to what has been observed off eastern Algiers on the rupture zone of the 2003 Mw 6.8 Boumerdes earthquake. The horizontal shortening rate across large folds is estimated to be of the order of 1 mm/yr. Although no historical earthquakes are reported here, these fault segments could have been responsible for large (M ~ 7.5) events in the past. This young tectonic system further supports the hypothesis of subduction inception of the Neogene oceanic lithosphere in the context of the Africa–Eurasia convergence

Searching for the Africa-eurasia Miocene Boundary offshore western algeria (Maradja'03 cruise)

International audienceWe present new results from the MARADJA'03 cruise depicting the geological structures offshore central and western Algeria. Using swath bathymetry and seismic reflection data, we map and discuss the offshore limits of the Internal Zones corresponding to relics of the AlKaPeCa domain that drifted and collided the African plate during the Miocene. We identify large reverse faults and folds that reactivate part of these limits and are still active today. The morphology of the westernmost NE–SW margin suggests a former strike-slip activity accommodating a westward block translation responsible for the shift of the Internal Zones towards the Moroccan Rif. To cite this article: A. Domzig et al., C. R. Geoscience 338 (2006). Nous présentons les résultats récents de la campagne MARADJA'03, qui visent à mettre en évidence les structures géologiques dans le domaine marin au nord-ouest de l'Algérie. Grâce aux données de bathymétrie multifaisceau et de sismique réflexion, nous cartographions et discutons les limites en mer des Zones internes correspondant aux reliques du domaine AlKaPeCa qui a dérivé, puis est entré en collision avec la plaque africaine au Miocène. De grandes failles inverses et plis, actifs dans le champ de contrainte actuel, réactivent certaines de ces limites. La marge ouest-algérienne, orientée NE–SW, indique la présence d'une ancienne activité en décrochement ayant accommodé la translation des Zones internes vers l'ouest

Increasing Control of Crustal Tectonics on Salt Tectonics from Mediterranean examples

International audienceThe deposition during the huge Messinian Salinity Crisis (MSC, 5.96 - 5.33 My) of a thick layer of evaporites and especially of a mobile halite unit (MU) has deeply influenced the architecture and evolution of the Mediter-ranean margins. The Mediterranean has characteristics that set it apart from most “classic” salt-bearing basins, where salt was deposited after (or right after) the rifting stage. Conversely, in the Mediterranean, salt was not related to a rifting event and it covers vast areas that are geodynamically active presently. These include regions of divergence (Tyrrhenian Sea), young or mature convergence (Algerian and Ligurian Margins, Ionian Sea, Mediterra-nean Ridge), oblique convergence (Eastern Cyprus Arc), and strike-slip (Levant Basin). Despite the progress in seismic processing, the strong acoustic impedance contrast between salt and sediments prevents an accu-rate seismic imaging of the sub-salt deep structures. Second, the evaporites act as a decoupling layer (thin-skinned tectonics) preventing the propaga-tion of the crustal structures towards the surface. Last, when crustal tecton-ics generates horizontal and vertical movements in the basement, these movements can trigger a gravitational response in the salt and its overbur-den, thereby blurring the deeper tectonic signal. In order to bypass these difficulties, we propose to use salt tectonics as a proxy to better constrain these deep structures both in terms of geometry and timing. Furthermore, the comparison between natural examples (seismic data) with analogue model-ling allows a better understanding of the margins’ structure and evolution. We present here a synthesis of several Mediterranean study cases in differ-ent geodynamical settings (divergence, convergence, strike-slip) with an in-creasing impact of the crustal tectonics on the salt tectonics. The complexi-ty and variety of its margins, along with the presence of a widely distribut-ed Messinian salt décollement, make the Mediterranean the perfect area to analyze salt deformation and its relationships with different tectonic styles, including the effects of crustal activity. Salt tectonics therefore provides a powerful tool to understand the deep crustal tectonics of the margins and to better constrain the timing of the crustal reactivation in the Mediterranean

Comparison of scaling properties of topography and bathymetry: the case of the Sardinia versus the Tyrrhenian Sea

International audienc

Utilisation de données Sparker monotrace à leur plein potentiel : une méthode simple pour investiguer des canyons sous-marins sur la plateforme continentale

International audienceLes données sismiques du Sparker fournissent des informations à Très Haute Résolution (THR) en mer, permettant une interprétation précise de la subsurface des eaux peu profondes à un coût relativement bas. Alors que de plus en plus de pays interdisent l'utilisation de la sismique de type air-gun sur leur territoire pour des raisons environnementales, l'utilisation du Sparker est souvent encore autorisée et son utilisation a considérablement augmenté au cours de la dernière décennie. Cependant, il n'est pas adapté aux eaux profondes. Il est nécessaire d'enregistrer des données avec un espacement de tir court pour obtenir une résolution et une qualité de données latérales optimales, ce qui permet une interprétation de la subsurface avec un niveau élevé de détails dans les séquences sédimentaires. Cet espacement court entre les tirs signifie également un court intervalle de temps entre les tirs, ce qui rend complexe l'imagerie à la fois des sédiments à haute résolution sur le plateau continental et des canyons sous-marins ou des vallées incisées le long d'une seule ligne de tir, car la trace sismique peut se terminer là où il y a encore un signal d'intérêt. Cela implique d'arrêter l'enregistrement pour changer les paramètres d'acquisition vers un intervalle de temps plus large, ce qui entraîne une perte de résolution horizontale et prend du temps. Pour tirer le meilleur parti des données du Sparker dans ces situations, nous avons développé une nouvelle méthode simple (SeeDeeper) qui permet l'interprétation des données THR pour des profondeurs d'eau plus importantes, permettant la création de sections sismiques de la partie la plus élevée du plateau continental jusqu'à la pente ou à travers des canyons profondément incisés. Cette étude vise à proposer un flux de traitement simple pour utiliser des données sismiques Sparker à leur plein potentiel. Dans l'étude de cas présentée, nous montrons plusieurs exemples qui démontrent l'intérêt d'une telle méthode. La méthode SeeDeeper nous a permis de suivre des discontinuités majeures et de connecter un ensemble de données sismique principalement situé sur le plateau continental à un jeu de données plus profond