Block tilting of the North Provence early Cretaceous carbonate margin: stratigraphic, sedimentologic and tectonic data

• Autores: J. P. Masse, Michel Villeneuve, Emmanuelle Leonforte, Jean Nizou
• Localización: Bulletin de la Société Géologique de France, ISSN 0037-9409, Vol. 180, Nº. 2, 2009, págs. 105-115
• Idioma: inglés
• Títulos paralelos:
  • Blocs basculés de la marge carbonatée nord-provençale au Crétacé inférieur: données stratigraphiques, sédimentologiques et tectoniques
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• Resumen
  • English

    In the western part of the Castellane tectonic arc, the so-called " Provence platform area ", corresponding to the foreland of the Alpine nappes (figs. 1-2), is marked by Tithonian-Berriasian shallow water carbonates capped by hemipelagic sediments deposited from the Valanginian up to the Aptian-Albian. A detailed biostratigraphic study of the Berriasian succession, based on calcareous algae and foraminifera, allows us to distinguish a Lower to Middle Berriasian, with Clypeina sulcata, Clypeina isabellae and Holosporella sarda, from an Upper Berriasian with Pfenderina neocomiensis, Danubiella cernavodensis, Falsolikanella campanensis and Macroporella praturloni (fig. 3). We performed a field survey of 30 sites located from Quinson to the west, and Escragnolles to the east (figs. 4-5) including the study of measured stratigraphic sections and the collection of samples for biostratigraphic interpretations. These stratigraphic investigations show that below the Valanginian beds, the Berriasian platfom carbonate succession, is locally incomplete, i.e. Upper Berriasian beds are frequently absent. During the Early and Middle Berriasian, depositional environments are marked by a strong bathymetric instability, with frequent subaerial exposure events, and a significant marine restriction; by contrast, during the Late Berriasian, the overall biological diversity increases and water agitation as well, which means a significant marine opening towards the basin. The Upper Berriasian hiatus is consequently regarded as the result of a Berriasian/Valanginian and/or a lowermost Valanginian erosion (fig. 6). The spatial distribution of complete or truncated Berriasian successions identifies east-west bands, in each band truncated series are located northward and complete series are located southward. Bands are limited by thrust or strip faults interpreted as palaeofaults reactivated during the Alpine orogeny (fig. 7). These fault-bounded blocks, 3 to 10 km in width, known as the Aiguine, La Palud-sur-Verdon, Carajuan-Audibergue and Peyroulles-La Foux blocks, are southerly rotated by 1 to 2o. We regard this structural architecture as the result of basinward tilting of blocks. Due to their rotation, the uplifted parts were eroded whereas the depressed parts were protected against erosion (fig. 8). Such a dynamic behavior reflects a distensive tectonic regime, which has been active at least during the Valanginian, that is after the drowning of the North-Provence carbonate platform. These structural events are considered as the regional expression of the Neocimmerian tectonic phase coupled with an enhancement of the Atlantic rifting. The orientation of the major Alpine structural elements (folds and faults) of the Castellane arc, is mostly inherited from these early Cretaceous tectonic events.

  • français

    L'avant-pays des nappes alpines de l'arc de Castellane (SE de la France) est caractérisé par des carbonates de plate-forme du Tithonien-Berriasien surmontés par des dépôts hémipélagiques développés du Valanginien à l'Aptien-Albien. L'analyse biostratigraphique et sédimentologique du Berriasien montre que la partie supérieure de cet étage est souvent absente. Lorsqu'ils sont présents, les dépôts correspondants représentent des milieux ouverts vers le bassin. La lacune du Berriasien supérieur est interprétée comme résultant d'une érosion datant de la limite Berriasien-Valanginien et/ou du Valanginien inférieur. La distribution dans l'espace des séries complètes ou incomplètes s'effectue suivant des bandes est-ouest, limitées par des failles chevauchantes ou décrochantes que nous considérons comme des accidents anciens réactivés durant les phases alpines. Ces bandes identifient des blocs affaissés de 1 à 2o vers le sud, suivant un dispositif paléostructural constitué de panneaux basculés vers le bassin, et mis en place en régime distensif. Ce régime qui a perduré après l'ennoiement de la plate-forme nord-provençale, doit être replacé dans le cadre de la phase tectonique néocimmérienne. Les principaux traits structuraux de la région, acquis au Tertiaire, sont en grande partie hérités de l'Eocrétacé.