Geodynamic evolution steps of the Mauléon Basin. A: Clansayesian (Uppermost Aptian) – Lower Albian: fracturing of the urgonian platform and major break down along the future Tardets Trough (orange color); starting of the West-Pyrenean diapiric process (1: Salies-de-Béarn; 2: Iholdy; 3: Arhansus; 4: Béloscare; 5: Saison complex; 6: Sarrance; 7: Lauriolle; 8: Lasseube). B : Upper Albian – Lower Cenomanian: creation of the Tardets-Sorholus Trough through W-E main counterclockwise strike slip inducing local extreme crust thinning and low N-S distension. Note the location of the transverse Saison and Barlanès listric faults and the present Chabalgoïty, Urdach, Bénou and Sarraillé outcropping mantle peridotites (black circles). C: Upper Cenomanian – Turonian: creation of the Mauléon Basin through widening of the Tardets-Sorholus Trough with dominant N-S extension and associated counterclockwise W-E strike slip weak motion. The sedimentary area increases laterally, both westward, beyond the Saint-Jean-Pied-de-Port fault to the Saint-Jean-de-Luz Basin and eastward, beyond the Ossau fault zone, to the eastern Bearn Basin. Note the development of the Turono-Coniacian Osquich Pass megaturbidite westward of the old Barlanès fault zone. D: Upper Eocene: Development through N-S compression of the pyrenean structures within the Mauléon Basin. The old Upper Cretaceous normal faults are reworked into E-W thrust faults (south verging in the southern Mendibelza-Igountze massifs and north verging in the northern North Pyrenean Frontal Thrust) and the old SW-NE transverse faults into dextral or anticlockwise strike slip faults. Note the strong northward offsetting of the Baygoura-Ursuya Massif along the transverse Pamplona Fault Zone.