Integrated geological study in an offshore renewable energy test site: a case from the Basque continental shelf (Bay of Biscay, Spain)

Abstract Testing and research centres for offshore renewable energy, exemplified by facilities like BIMEP (Biscay Marine Energy Platform) on the Basque coast of Spain, play a crucial role in driving the energy transition. This study utilises pre-existing data at the facility site, such as high-resolution bathymetry and granulometric information from sediment samples, to conduct a comprehensive geological analysis including both sedimentary and rocky seabed. A litho-structural analysis is presented, including a lithological prediction for the continental shelf, the recognition of the main structures, such as NW-trending folds and predominantly NE-SW oriented fractures, and a detailed fracture analysis. Sedimentary seabeds are analysed through a Seabed Sediment Map, illustrating a granulometry-based NE-SW oriented banded distribution. Bedforms are also studied, they are asymmetric and mainly oriented NE-SW. The Seabed Sediment Map and the bedform analysis reveal the effect of an SE-directed bottom current as the main mechanism controlling sediment mobility. This current matches with the predominant swell from the NW and with the direction of the most energetic waves in the area. This approach could serve as a methodological example, offering a cost-effective means for the preliminary geological characterisation of offshore energy sites, and is crucial for establishing a baseline (‘zero state’) before the deployment. This baseline is essential for evaluating and mitigating the impact of new infrastructure on sediment dynamics, which subsequently affects the overall functioning and health of the marine ecosystem.