Campagne CYADANOIS. 9-22 juillet 1979

The submersible Cyana dives in the Bay of Biscay during sununer 1979, in order to study the stratigraphy and the structure of the northern Spanish continental margin. Data collected during the cruise are presented: analysis of fifty rock samples, photographs of the submarine rock outcrops, geological sections along each path of Cyana on the sea floor. The main results are outlined. An accurate reconstruction of the stratigraphical sequence shows the ante-Mesozoic basement, Jurassic and earliest-Cretaceous limestones and early Cretaceous sandstones and conglomerates. We explain the existing structural trends on the continental slope by the following tectonic evolution: an early Cenozoic compressive phasis induces the formation of an imbricated structure, involving the continental basement and the sedimentary caver. Further phases of normal and transcurrent faulting give the present morphology.Le submersible Cyana a permis, en 1979, d'étudier la stratigraphie et la structure de la marge continentale nord-espagnole dans le golfe de Gasco­gne. Ce mémoire contient les données recueillies pendant la campagne de plon­gée : analyse des échantillons prélevés; photographies des affleurements ro­cheux; coupes géologiques selon chaque trajet du submersible. Ces données sont précédées par une présentation des principaux résultats scientifiques de la campagne. La stratigraphie de la marge est détaillée : socle antéméso­zoique; sédiments carbonatés du Jurassique et du Crétacé basal; flyschs, grès et conglomérats du Crétacé inférieur. La structure actuelle est expliquée par la succession tectonique suivante : écaillage du socle et de sa couverture au début du Tertiaire; distension et cisaillements ultérieurs

Cinématique de l'Est Indonésien depuis le Miocène Moyen

National audienceL’Est Indonésien est situé à l’intersection des trois grandes plaques Eurasie, Pacifique et Indo-Australie. Depuis 1978, pas moins de quinze modèles géodynamiques différents impliquant, à des échelles variées, l’Indonésie orientale, ont été proposés. Cependant aucun ne prend en compte la présence d’une lithosphère océanique entrée en subduction dans la fosse de Séram et plongeant jusqu’à 500 km de profondeur dans le manteau. La plupart de ces modèles ignorent aussi l’âge Néogène Supérieur des bassins rencontrés dans la région de la Mer de Banda.De récentes études géochimiques et géochronologiques ont montré que la Mer de Banda Sud s’était ouverte entre 6 et 3 Ma en arrière de la subduction de la plaque australienne vers le Nord sous l’arc de Banda. Ceci est confirmé par les anomalies magnétiques identifiées dans le bassin. Dans la Mer de Banda Nord, les données magnétiques et géochronologiques s’accordent avec une ouverture du bassin entre 12 et 7 Ma. Enfin le Bassin de Weber à l’Est se serait ouvert au Plio-Quaternaire dans un contexte de collision oblique.En considérant ces nouvelles données, nous proposons un modèle d’évolution géodynamique de l’Indonésie orientale pour les quinze derniers millions d’années. Nous utilisons les anomalies magnétiques reconnues en Mer de Banda pour refermer successivement le Bassin Sud Banda entre 3 et 6 Ma et le Bassin Nord Banda entre 7 et 12 Ma, tout en respectant les mouvements des grandes plaques environnantes. Enfin notre reconstitution intègre l’existence de microcontinents d’origine australienne aujourd’hui dispersés dans la région de Banda. Avant leur séparation au Néogène Supérieur, une partie de ceux-ci étaient rassemblés en un microcontinent unique, le Bloc de Banda

Late Cenozoic geodynamic evolution of eastern Indonesia

International audienceThis paper presents an internally and globally consistent model of plate evolution in eastern Indonesia from Middle Miocene to Present time. It is centered on the Banda Sea region located in the triple junction area between the Pacific–Philippine, Australia and South–East Asia plates. The geological and geophysical data available from Indonesia were until recently insufficient to define a unique plate tectonic model. In this paper, the new data taken into account clearly restrict the possible interpretations. Owing to a great number of geological, geophysical and geochemical studies, the major plate boundaries (the Sunda–Banda subduction zone to the south, the Tarera–Aiduna Fault zone and the Seram Thrust to the east, and the Sorong Fault zone and Molucca Sea collision zone to the north) are now clearly identified. The age of the major tectonic structures isalso better known. Geodetic measurements well constrain the Present time plate kinematics. We also consider the deformation history within eastern Indonesia, where numerous short-lived microplates and their related microcontinents successively accreted to the Asiatic margin. Moreover, magnetic anomalies identification of the North and South Banda Sea basins allows a precise kinematic reconstruction of the back-arc opening. We used the Plates software to test the coherency of our model, presented as a series of 4 plate reconstruction maps from 13 Ma to the present. Finally, the origin of oceanic domains restored by our reconstruction is discussed

Origine et évolution du bassin Nord-Banda (Indonésie) : apport des données magnétiques

International audienceThe North Banda Sea Basin is located in Eastern Indonesia, close to the triple junction between the Eurasian, Pacific and Indo-Australian plates, andopened during Late Miocene time in a back arc setting. We use the magnetic and bathymetric data to depict this opening and the geodynamical evolution of the basin. We also take into account radiochronological datations available from some dredges of its basement. Sea floor spreading occurred from 12.5 to 7.15 Ma directed by three large NW–SE transform faults, namely the West Buru, Tampomas and Hamilton fracture zones. Finally, a schematic model of the North and South Banda basins evolution is presented.Le bassin Nord-Banda, situé en Indonésie orientale à proximité du point triple entre les plaques Eurasie, Pacifique et Indo-Australie, s’est formé au Miocène supérieur dans un contexte arrière-arc. Nous utilisons les données magnétiques et bathymétriques pour préciser la géométrie de l’ouverture du bassin et retracer les grandes étapes de son évolution géodynamique. Nous prenons aussi en compte les datations du plancher océanique obtenues à partir de dragages. L’accrétion océanique s’est déroulée entre 12,5 et 7,15 Ma suivant une direction NW–SE. L’ouverture du bassin fut guidée par les grands accidents transformants de Buru ouest, de Tampomas et de Hamilton. Un modèle schématique de l’évolution des bassins Nord et Sud-Banda est enfin présenté

Oligocene reefal deposits in the Pisang Ridge and the origin of the Lucipara Block (Banda Sea, eastern Indonesia)

International audienceIn 1998 we dredged early Oligocene/late Oligocene boundary, shallow-water reefal deposits and pelagic, early Pliocene muds in the submerged Pisang Ridge. The shallow-water deposits were identified as moderate- to low-energy coral-reef depositional environments, which confirms that the PisangRidg e belonged to the continental to continental-arc Lucipara Block which also includes the TukangBesi, Lucipara and Rama ridges. On the basis of these findings, it was possible to reconstruct parts of the general geological evolution of the Lucipara Block, which drifted away from northern Irian Jaya duringmid- Miocene times and collided with the Kolonodale Block during the late Miocene. A late-early Oligocene calc alkaline volcanic arc developed in the Weber Trough area, then uplifted to a shallow-water position at the early–late Oligocene boundary in the Pisang Ridge. Late Oligocene–early Miocene metamorphism subsequently developed, prior to the deposition of early Miocene coral reefs in the Rama Ridge. Locally, late Miocene metamorphism was identified in the Lucipara Ridge, prior to the latest Miocene–Pliocene general drowning and the splitting of the Lucipara Block into several small blocks throughout the Banda Sea region

A Neogene back-arc origin for the Banda Sea basins: geochemical and geochronological constraints from the Banda ridges (East Indonesia)

International audienc

Impact of lower plate structure on upper plate deformation at the NW Sumatran convergent margin from seafloor morphology

We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysis of the combined dataset accurately highlights those portions of the seafloor shaped by active tectonic, depositional and/or erosional processes. The greatest slope gradients are located in the frontal 30 km of the forearc, at the toe of the accretionary wedge. This suggests that long-term deformation rates are highest here and that probably only minor amounts of slip are accommodated by other thrust faults further landward. Obvious N–S oriented lineaments observed on the incoming oceanic plate are aligned sub-parallel to the fracture zones associated with the Wharton fossil spreading center. Active strike-slip motion is suggested by recent deformation with up to 20–30 m of vertical offset. The intersection of these N–S elongated bathymetric scarps with the accretionary wedge partly controls the geometry of thrust anticlines and the location of erosional features (e.g. slide scars, canyons) at the wedge toe. Our interpretation suggests that these N–S lineaments have a significant impact on the oceanic plate, the toe of the wedge and further landward in the wedge. Finally, the bathymetric data indicate that folding at the front of the accretionary wedge occurs primarily along landward-vergent (seaward-dipping) thrusts, an unusual style in accretionary wedges worldwide. The N–S elongated lineaments locally act as boundaries between zones with predominant seaward versus landward vergence.<br/