Complex sentence: The outer perimeter is a circular inward scarp about 12 km in diameter on the largely undisturbed Cretaceous and upper Silurian sediments of the Parnaíba basin, breached on the west, north, and south sides by drainage valleys.
Split into simpler sentences: The outer perimeter is a circular inward scarp about 12 km in diameter, on the largely undisturbed Cretaceous and upper Silurian sediments of the Parnaíba basin. The perimeter is interrupted on the west, north, and south sides by drainage valleys.