Géosciences Montpellier

• Planète et Univers/Sciences de la Terre/Stratigraphie
  
• Planète et Univers/Sciences de la Terre/Tectonique
  
• Planète et Univers/Sciences de la Terre
  
• Planète et Univers/Sciences de la Terre/Géologie appliquée
  
• Planète et Univers/Sciences de la Terre/Océanographie
  
• Sciences de l'environnement/Biodiversité et Ecologie
  
• Planète et Univers/Sciences de la Terre/Paléontologie
  
• Planète et Univers/Sciences de la Terre/Volcanologie
  
• Planète et Univers
  
• Planète et Univers/Sciences de la Terre/Géochimie
  
• Sciences de l'environnement/Milieux et Changements globaux
  
• Sciences du Vivant/Biodiversité/Systématique, phylogénie et taxonomie
  
• Planète et Univers/Sciences de la Terre/Géomorphologie
  
• Planète et Univers/Sciences de la Terre/Géophysique
  
• Physique/Physique/Géophysique
  
• Planète et Univers/Interfaces continentales, environnement
  
• Sciences de l'Homme et Société/Etudes de l'environnement
  
• Sciences de l'environnement
  

This study investigates the Lesser Antilles fore-arc at the latitude of Guadeloupe Archipelago and evidences that La Désirade Island, the eastermost island of the forearc, displays a staircase coastal sequence including four uplifted marine terraces and an upper reefal platform with mean shoreline angle elevations ranging from 10 to 210 m above sea level (asl). The platform paleobathymetry is constraint by a detailed analysis of the sediments. We propose a revised morphostratigraphy for this coastal sequence including 5 paleo-shorelines based on six U/Th dating from aragonitic corals from the three lowest terraces combined with paleobathymetric analysis of the fossil corals present in the upper platform. Terrace and upper platform carving of construction periods occurred during Marine Isotopic Stages MIS 5e, MIS 9, and during the intervals MIS 15–17, MIS 19–25 and MIS 31–49 (upper coral reef platform). Our results evidence a bulk decreasing uplift rate since early Calabrian to Present-Day, clearly documented since 310 ka (MIS 9) (from 0.14 to 0.19 to ca 0 mm/y). Our data are consistent with first the transient influence of the subducting oceanic Tiburon ridge during Calabrian, then with other parametres of the subduction zone since late Calabrian to Present-Day (dip of the slab, basal erosion of the upper plate, inherited structures …).

During the Messinian Salinity Crisis (MSC), between 5.97 and 5.33 Ma, the marine connections between the Atlantic Ocean and the Mediterranean Sea were temporarily restricted. The post-MSC reflooding of the Mediterranean Sea by the Atlantic waters and its sedimentary record are debated. The Boudinar basin (North-Morocco) provides an exceptional record of this period between ca 5.32–5.27 and 4.37 Ma at youngest (Zanclean - Zone PL1). The sedimentary succession of this basin comprises seven facies associations corresponding to depositional settings ranging from continental to open marine environments.We provide a new sequence stratigraphic framework, based on twelve stratigraphic sections. Two orders of depositional sequences (4th, 3rd order), related to base-level changes during the Late-Messinian Early-Pliocene time interval, are correlated at the basin scale. According to our reconstruction, the post-MSC base level rise and the Zanclean reflooding lasted from a minimum of several tens up to hundreds thousands years, suggesting a gradual, not catastrophic event indicative of a progressive transgression.

The sedimentary model of coastal deposits in eastern Rhodes over the last 2 Ma is refined and improved in accuracy. New field investigations and U/Th dating of Spondylus bivalve shells, combined with micropalaeontological and sedimentological data, allow the recognition of four synthems separated by major erosional surfaces. We present here evidence for two of these erosional surfaces. This new model allows the identification and quantification of the vertical movements recorded by the studied exposures. The history of these vertical motions is characterized by two periods of uplift and two periods of subsidence. Such an evolution is unique at the regional scale in the eastern Hellenic forearc. We interpret these results as reflecting the individualization of Rhodes as a single tectonic block during increasing trench bending. This trench bending is accommodated by an increase in the curvature of the forearc during the last 2 Ma.

The Cap des Trois Fourches (Eastern Rif, northern Morocco) metamorphic basement exposes two major tectonic units, namely the Taïdant unit underthrusting the overlying Tarjât tectonic unit. The Tarjât tectonic unit is composed of metamorphic rock originating from detrital material. This upper Tarjât tectonic unit exhibits: (1) orthogneiss bodies being Paleozoic in age and (2) evidences showing a retromorphose during the Alpine orogenesis. U-Pb SHRIMP zircon geochronology from the orthogneiss bodies has yielded Sakmarian (early Permian) ages for the intrusion of their protoliths. The lower Taïdant unit is formed of green and brown shales associated with quartzite beds. A Mesozoic age is commonly accepted for this unit.The internal structure of the Tarjât tectonic unit consists in km-scale folds trending ENE-WSW with an up-dip direction towards the SE. This compressional deformational stage was superimposed on internal thrust sheets controlled by ductile shear zones with a SW-vergent transport sense. The lower Taïdant unit shows conspicuous bedding associated with a penetrative foliation outlining a monocline structure dipping gently towards the NW. The major ductile-brittle detachment fault bounding the upper Tarjât tectonic unit from the lower Taïdant unit –i.e. the local basement– exhibits evidences for a top-to-the-west sense of motion. We assume that this specific fault is the prolongation into the Cap des Trois Fourches area of the extensional detachment previously described in the Temsamane area. Therefore, this low angle detachment fault is a major tectonic element extending hundreds of km through the Eastern Rif. We postulate that this major detachment roots deep in the Eastern Rif basement. This detachment is cut at the surface by the Nekor normal-sinistral strike-slip fault that separates thin 24–32 km thick metamorphic Eastern Rif crust from the 50–55 km thick crust of the Western Rif. This transtensive fault system exhumes the Rif middle crust, represented by the Temsamane massif units, along the Nekor sinistral STEP boundary at the southern edge of the Betic-Rif subduction system.

Carte Géologique Terre-Mer La réalisation de la carte géologique du plateau continental de Basse-Provence repose sur l’interprétation de profils de sismique réflexion 2D et sur l’intégration d’échantillons de roches prélevés sur le fond marin par dragage et carottage et présente un essai de corrélation entre la cartographie géologique à terre et celle du plateau continental. Cette nouvelle carte géologique du plateau continental représente les formations anté-quaternaires affleurant sur le fond marin ou très faiblement recouvertes de sédiments plio-quaternaires (épaisseur inférieure à 10ms.t.d.,milliseconde temps-double). La formation -114-d’âge Plio-Quaternaire a été intégrée à la carte géologique uniquement lorsque son épaisseur dépasse les 10ms.t.d., soit environ 8m (avec une vitesse sismique de 1700m/s.