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

Saint Barthélemy is the only island of the northern Lesser Antilles where it is possible to investigate in the detail the chronostratigraphy of the mixed carbonate-volcaniclastic deposits of the Paleogene Caribbean volcanic arc. Based on field mapping and new biostratigraphical and sedimentological data, we study the limestone units interbedded in the Paleogene volcaniclastic deposits. We find that four main carbonate units occur instead of previously believed six ones. Based on the ages given by the foraminifera assemblages, and taking into account the recently published 40Ar/39Ar ages of magmatic rocks, the Lower Limestone unit dates Lutetian, the Intermediate Limestone unit late (?) Bartonian-late Priabonian, the Upper Limestone late Priabonian and the Top Limestone unit early Miocene. The Paleogene carbonate beds were deposited on gently dipping submarine volcaniclastic deposits issued from emergent volcanoes, in muddy, unrimmed inner to mid-ramp setting dominated by bottom communities. A major subaerial unconformity is evidenced during the Oligocene, most probably corresponding to uplift affecting Saint Barthélemy. Our work offers a revised lithostratigraphic succession of Saint Barthélemy as a first key-point for further studies of the Paleogene Caribbean arc deposits which were dismembered following the entrance of the Bahamas Bank in the Lesser Antilles subduction zone.

Dans le Rif interne (domaine d’Alboran), le massif de Beni Bousera expose un empilement de péridotites et d’unités métamorphiques crustales. Ce massif est recoupé par des filons granitiques et affecté par plusieurs zones de cisaillement ductiles normales. Des analyses structurales, pétrologiques et des datations 40Ar–39Ar réalisées sur ces deux types d’objets montrent que, (1) les filons granitiques se sont mis en place dans des zones de failles et des zones de cisaillement normales, orientées en majorité entre N70° à N140° résultant d’une extension NNE-SSW, (2) la faille d’Aaraben dans sa partie NE est caractérisée par des zones de cisaillement ductiles normales, orientées N70° à N150° résultant d’une extension N-S et (3) l’âge de cet évènement extensif est compris entre 22 et 20 Ma. Les données paléomagnétiques disponibles, permettent de restaurer l’orientation initiale de cette extension, qui était approximativement E-O contemporaine de l’ouverture du bassin d’Alboran en position d’arrière-arc, au cours du Miocène inférieur. Au début de l’extension, les péridotites reposaient sur une croûte continentale partiellement fondue, et exhumées pendant cet évènement par la zone de cisaillement normale d’Aaraben. Le domaine d’Alboran a ensuite été affecté par plusieurs événements compressifs.

As subduction zones and their related processes are often studied in 2D, or cylindrical 3D sections, the dynamic effects of trench curvature and its evolution through time remain under-explored. Whereas temporal variations in trench trend may be estimated through restoring upper plate deformation, we investigate the forearc deformation history of the strongly curved northern Lesser Antilles trench, connecting the near-orthogonal Lesser Antilles subduction zone with the Motagua-Cayman transform plate boundary. Our new paleomagnetic dataset consists of 310 cores from Eo-Oligocene magmatic rocks and limestones from St. Barthélemy Island. The limestones yielded a post-folding magnetization containing a similar magnetic direction to those stored in magmatic rocks that intrude the folded carbonates, both indicating a post-Oligocene ~15°, and perhaps up to 25° counterclockwise rotation of the island. Our results highlight that the present-day trench curvature formed progressively during the Cenozoic, allowing us to discuss different tectonic scenarios explaining NE Caribbean plate deformation, and to identify key targets for future research on tectonic architecture and the potential present-day activity of intra-plate deformation that may pose seismic hazards.

By their past and present diversity, rodents are among the richest components of Caribbean land mammals. Many of these became extinct recently. Causes of their extirpation, their phylogenetic affinities, the timing of their arrival in the West Indies, and their biogeographical history are all ongoing debated issues. Here we report the discovery of dental remains from lower Oligocene deposits (~29.5 Ma) of Puerto Rico. Their morphology attests to the presence of two distinct species of chinchilloid caviomorphs, closely related to dinomyids in a phylogenetic analysis, and thus of undisputable South American origin. These fossils represent the earliest Caribbean rodents known thus far. They could extend back to 30 Ma the lineages of some recently-extinct Caribbean giant rodents (Elasmodontomys and Amblyrhiza), which are also retrieved here as chinchilloids. This new find has substantial biogeographical implications since it demonstrates an early dispersal of land mammals from South America to the West Indies, perhaps via the emergence of the Aves Ridge that occurred ca. 35–33 Ma (GAARlandia hypothesis). Considering both this new palaeontological evidence and recent molecular divergence estimates, the natural colonisation of the West Indies by rodents likely occurred through multiple and time-staggered dispersal events (chinchilloids, then echimyid octodontoids [spiny rats/hutias], caviids, and lastly oryzomyin muroids [rice rats]).

In the frame of the GAARAnti ANR-17-CE31-0009 project, we aim at establishing the paleogeography of the arc/forearc areas of the Northern Lesser Antilles over the last 35 Ma to bring constraints for the mammal fauna dispersion paleo-biogeographic models from south America to Greater Antilles. Available paleogeographic maps are ancient (Stephan et al., 1990; Iturralde-Vinent & McPhee, 1999) and contradictive. During that time, the forearc of the Lesser Antilles subduction zone strain pattern accommodated (i) strain partitioning related to subduction obliquity and (ii) progressive trench bending by several episodes of differential vertical and horizontal motions which may have built and/or destroyed continental areas allowing south american terrestrial mammals to reach the Greater Antilles or isolating some south American mammals on newly formed islands. We conducted new studies, onshore on the Anguilla Bank islands and offshore in Kallinago Trough and Wallichi Plateau to reconstruct the evolving paleogeography of this area. We used: 1) new micropaleontological, sedimentological and paleoenvironmental results acquired onshore and from dredged samples during the GARANTI Cruise in may 2017; 2) a database of seismic profiles from various sources: CPEM 1980; ANTITHESIS 2016 and GARANTI 2017 cruises.Onshore, we revised the stratigraphy of the Neogene series. Offshore, we established a seismic stratigraphy and correlated the seismic units and erosional unconformities with the onshore lithostratigraphic successions. We then built paleogeographic maps for different time spans: late Eocene-early Oligocene, late Oligocene-Aquitanian, Burdigalian, early Langhian, mid-late Miocene and Zanclean. During late Eocene-early Oligocene most the area was emergent except in the Kallinago Trough. Significant subsidence periods occurred during Burdigalian and mid-late Miocene and most of the terrestrial areas were drowned. During early Langhian and Zanclean numerous small islands occurred.