The Eocene Ainsa Basin is situated in the central south Pyrenees formed by collision of the Iberian plate with the Eurasien plate during Late Cretaceous to early Miocene times. The basin was formed due to movements of the central southern Pyrenean thrust system in a piggy-back fashion. The depositional system was controlled by the Mediano growth fold and the Faradada tear fault system. The climate was a secondary factor controlling the sea-level variations (Milancovich cycles). These controlling factors have been reflected in the recorded data gathered in the Arro and Charo areas (Arro sandstone body. The succession can be divided into 4 distinct units; a basal mass transport complex, an inter-channel dominating succession, a turbidite channel succession, and a channel-levee dominated succession. This may reflect a system that has been triggered by tectonism and subsequently formed instabilities on the ramp of the basin. The relative sea-level may have been influenced by movement of the structures described above, and subsequently gradients in the depositional system from the source area in the Pyrenean axial zone to the deep marine Ainsa Basin. This is reflected in the progradation of the Montanana delta and the San Eseban fandelta. Palaeo-current trends give a NNW direction of the deep marine depositional ramp system.