The Massif d'Igountze–Mendibelza, western Pyrenees, is a fault-bounded block of Palaeozoic basement overlain by an exceptionally thick Cretaceous siliciclastic sequence. North of the Massif, the Cretaceous sequence conformably overlies Lower Cretaceous carbonates, yet, immediately south of the Massif, it is entirely absent. The sequence fines northward and has NNE palaeotransport. The basement is commonly brecciated near the contact with the sedimentary cover, and the uppermost beds dip less steeply than the lowermost. These tectono-stratigraphic relationships are best explained by Cretaceous deposition above a relatively low-angle normal fault.
The Cretaceous deposits of the Massif d'Igountze–Mendibelza are part of the western extension of the North Pyrenean basin, a basin or series of sub-basins that began to form in the latest Aptian to Albian north of and along most of the length of the North Pyrenean fault. The precise relationship between deposition on the Massif and in the rest of the North Pyrenean basin is not known. There may have been many local variations in stress regime and structural style along the basin or sub-basins, but the regional episode of basin formation was a result of the same plate-reorganizational event. Later basin inversion was due to the latest Cretaceous to Eocene Pyrenean orogeny.