The area of the Iullemmeden Basin seems to have started to subside in Permo-Triassic times, and to have experienced gradual downwarping during the Late Cretaceous to Paleogene times, while steadily filling with sediment. Two prominent fault trends run NNE-SSW through the center of the basin, while WSW-ENE faults trends are found in the northeast of the basin near the Aïr Mountains.[1]