Clastic sedimentary basins have evolved during the past 40 m.y. in the central Andes (lat. 20°-28°S) in response to shifting patterns of magmatism and deformation. The distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the North American Rocky Mountains during the Late Cretaceous and early Cenozoic. Petroleum exploration has focused on zones underlying the upper Cenozoic strata along the eastern margin of the Andes mountain belt.

Between about 40 and 25 Ma, a nonmarine basin extended across the region that is now the Andes Mountains. Between about 25 and 10 Ma, the western part of the former basin became the site of a volcanic arc; sediment accumulation continued in the east, where marine intercalations demonstrate the low elevation of the basin. After 10 Ma, the volcanic arc remained active and locally widened, and crustal shortening caused regionally important thrust and reverse faulted ranges. During the past 10 m.y., up to 4,000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains; meanwhile in the interior of the mountains, over 4,000 m of fine-grained strata and evaporites accumulated in local depocenters.