The "GIROPAL" (GIRonde PALéogène) high-resolution oceanographic seismic acquisition campaign aims to image Paleogene geological formations and identify the various deformations recorded during this period on the northern Aquitaine shelf off the Gironde estuary, located at the southern end of the Armorican shelf and the eastern end of the Bay of Biscay. Its aim is to improve geological knowledge of the France continental shelves, and more specifically to study the Tertiary of the southern Armorican continental shelf, in the extension of the Aquitaine Basin.

There are few seismic data available for the Paleogene and its relationship with the underlying Mesozoic on the northern Aquitaine plateau. This period, which is synchronous with the Iberian-European convergence, is nonetheless crucial, as it is the period during which landscapes are totally remodeled in line with tectonic deformation. The acquisition campaign therefore targets the Paleogene formations of the Nord-Aquitaine region.

Analysis of the geometry of the sedimentary filling and the tectonic structures of the North Aquitaine shelf would make it possible to :

• Prioritize deformations and identify the style and age of these deformations; 
• Quantify the vertical movements induced;
• Define the nature and geometry of sedimentary systems and their evolution over time in relation to these deformations.

The results will be compared with the deformation styles of neighbouring domains, from the northern Armorican shelf to the Parentis basin, and from the Bay of Biscay abyssal plain to the Aquitaine basin, for integration on a regional scale as part of the OROGEN(1) research project.

To best image the Paleogene of the northern Aquitaine shelf off the Gironde river, we propose to acquire high-resolution seismic profiles. Interpretation of the GIROPAL seismic grid will complement or provide new information on :

• The location and style of tectonic structures affecting the Tertiary bedrock;
• A hierarchy of tectonic events and a deformation calendar;
• the spatial distribution of zones of uplift or subsidence;
• the transition from Mesozoic to Tertiary formations south of Oléron, to better identify terminal Cretaceous-basal Palaeogene deformation;
• major surface geometries and directions of major sedimentary inputs (major erosions and floods) to determine the paleogeographic and morpho-structural evolution of the area;
• Mio-Pliocene incisions observed on the outer North Aquitaine plateau by Bellec (2003). These data will also be used to determine the course of the large filled incisions observed off Rochebonne (GEOVEND profiles, Huerta et al., 2010).