Surface and subsurface geology of the Hontomín structure, Western Pyrenees

A detailed geological study was conducted in the Hontomín area in the western Pyrenees,Northern Spain, focusing on structural characterization by integrating available subsurfacedata with a newly developed surface geological map. It reveals a relatively simple surfacestructure, with the Upper Cretaceous generally dipping gently eastward, except at thesouthern margin, where they are deformed into tight E-W-trending folds. In contrast,the unconformable Cenozoic layers dip only a few degrees southward. However, seismicdata interpretation reveals a much more complex subsurface structure. It is dominatedby a broad dome, cored by Upper Triassic salt, which has significantly influenced theoverlying stratigraphy and structure. Above the salt, the Jurassic and Lower Cretaceousunits exhibit moderate folding, a deformation style that is not apparent at the surface.The deep structure is controlled by a major E-W trending thrust fault, which is notclearly expressed at surface except through small-scale, tight folds aligned in the samedirection. This study highlights the importance of integrating surface mapping withgeophysical data, both for accurately interpreting subsurface geology when planning forCO₂ injection operations.