Geophysical Exploration of Archaeo-palaeontological cave sites by Electrical Resistivity Tomography : A Case Study of Baio Cave, N Spain

The Electrical Resistivity Tomography (ERT), a method based on the differences in electrical response of different geological materials, has multiple applications in complementary fields such as Geology, Archeology and Paleontology. Examples of this application include the exploration and delimitation of buried anthropic structures or assessing the geometry of cave galleries.

The Baio cave site has yielded a restricted yet interesting fossil record on its surface providing interesting climatic information regarding the Middle-Upper Paleolithic transition. Additionally, despite its restricted length (< 30 m), the cave contains a rich paleontological sedimentary deposit of approximately 6 m predominantly composed of cave bears. Whether the current known extension of the cave represents the actual extension of the galleries, and/or whether additional caves are represented in the adjacent sectors of the Baio cave is an interesting matter due to their potential archaeo-palaeontological content and geological information towards understanding cave formation processes in this area. Thus, with the aim of gaining information on their possible orientation and location of new galleries/caves, a comprehensive and multifaceted multiscale study has been carried out on the basis of a detailed ERT investigation around the Baio cave supported by the characterization of the main orientation fracture networks on the local and regional scale.

The collected structural data consistently indicate the presence of four main fracture systems across all scales showing approximately the following trends: N020E, N060E, N105E and N160E. These preferred orientations are interpreted as longitudinal, transverse and oblique discontinuity surfaces associated to folding processes responsible for the main geological structures within the Basque Arc domain of the Basque-Cantabrian Basin. These orientations hold significant promise for locating new caves with potential archaeo-palaeontogical record, suggesting avenues for exploration. In fact, these measures are in complete accord with the trends of maximum anomalies recognized in the ERT profiles performed around the Baio cave (N020E, N065E and N107E and N160E directions), interpreted as partially or full air-filled galleries or cavities. These cavities, located at depths not exceeding 5 meters from the surface, might be considered as possible candidates in order to complete the archaeo-palaeontological research in progress.