The Mesozoic and Cenozoic paleodrainage of South America: a natural history

The drainage history of South America, since its breakup and separation from Africa about 100 Ma, shows an exceptionally compelling and pervasive tectonic control that should be true of all the continents, disruption by continental ice sheets excluded. lly all of South Americaʹs present major drainage developed after its separation from Africa. First, broad domes and aulacogens affected rivers such as the lower Amazon, the São Francisco, Uruguay, Rio de la Plata and their tributaries, and the Colorado and Negro in Argentina. Later the Mid-Miocene uplift of the Andes greatly enlarged the Amazon system and also created the present Magdalena and Paraguay Rivers and most of the Orinoco System. Of all these the Amazon is unique in that its “Andean event” can be dated both at its headwaters and offshore. Of all the major South American rivers, the Paraná seems to have the most perfect adjustment to structure, and probably developed after outpouring of the Serra Geral basalts in the late Cretaceous. Examination of the offshore record of South Americaʹs passive margin contributed significantly to this analysis, although megashears, plate convergence and impinging oceanic currents have destroyed the offshore record of many rivers. s era of global geology the ages and paleodrainage of entire continents deserve far more attention from the geologic community than they have received.