The geological map and the structural cross-sections presented here show the northern part of the South Pyrenean fold and thrust belt located west of the termination of the axial zone. The structures show a ~ SSW vergence, with a rotation of the structural axes from NNW-SSE in the north, to WNW-ESE in the south. The sediments in this area have been deposited syntectonically and have been deformed during two main phases of deformation.
The first phase of deformation (D1) is related to the Lakhoura basement thrust, which separates the North Pyrenean zone in the north and the axial zone in the south. This deformation phase can be subdivided into 3 sub-phases, the first one related to the Lakhoura thrust (D1a), the second to the Larra thrust (D1b) and the third to the reactivation of the Lakhoura thrust (D1c). Both the Lakhoura thrust and the Larra thrust branch of the Lakhoura basement thrust. The Lakhoura thrust has a décollement level in the lower part of the Ochogorri formation from which a few thrusts branch of in this formation. The Ardibidipicua thrusts are the result of the reactivation of the Lakhoura thrust (D1c). The Larra thrust has a décollement level in the incompetent sediments of the Couche Rouge formation. An important structure is the Urzainqui fault propagation fold, which shows synsedimentary activity during deposition of the Roncal turbidites. It forms several other thrusts, where the most important ones are the Zardaya, Inzaga and Cacueta thrusts.
The second phase (D2) is related to the formation of the axial zone, which resulted from thrusting along the Gavarnie basement thrust. In this area, the structures related to this thrust shows some upright to overturned folding and related steep reverse faulting in the Mesozoic-Cenozoic cover sediments of the Hercynian basement. The most important structures are the Arniota, San Zolo and Ezcaurri anticlines and the Ardibidipicua syncline. The fold axes related to this phase plunge towards the WNW, where the plunge decreases from ~ 30° in the north (located above the axial zone) to ~ 0° in the south (located south of the axial zone).
A minimum amount of shortening of some 16.5 km can be derived from the constructed cross-sections. About 3.5 km of this total amount can be attributed to the Lakhoura thrust (D1a and D1c) Some 8.0 km of the total amount of shortening can be attributed to the Larra thrust (D1b). The remaining 5.0 km can be attributed to the Gavarnie thrust (D2).
The sedimentation of this area of research is strongly influenced by the tectonic activity with the development of a foreland basin in the south and the formation of thrust sheets in the north. During evolution of the basin, progressive thrusting from the north resulted in the shifting of the foreland basin towards the south, where turbiditic sediments of Eocene age show onlapping geometries towards the south over a drowned Paleocene carbonate platform. The work suits with the general ideas about the development of the paleo-foredeep of the southern Pyrenees, its syntectonic sedimentation and its structural development into becoming a foreland fold and thrust belt. However, although most thrusts probably developed in an in-sequence order, evidence suggests that some thrusts (Ardibidipicua thrusts) developed during out-of-sequence thrusting.