As the western portion of Gondwana in the late Palaeozoic, South America extended over a great range of palaeolatitudes, from southern polar to tropical. At the time of the global lowering of temperature that triggered the “ice age,” strong climatic differences became established between those extreme palaeolatitudes. The portion that was close to the southern palaeopole had low temperatures and was covered by ice sheets; the rest of the continent, which was at lower palaeolatitudes, had higher temperatures (Figure 25.1).

As was the case in the Cenozoic, late Palaeozoic glaciation in South America encompassed several glacial and interglacial stages. In western and southern Argentina, evidence of that glaciation is widespread in sediments whose dates range from as old as Visean–Namurian to as young as late Asselian. Discrimination of discrete glacial stages has been based on striated pavements covered with diamictites and associated varved sediments, dropstone laminites, and so forth (Frakes, Amos, and Crowell, 1969; López Gamundi and Amos, 1983; González, 1983). Sections that afforded doubtful or questionable evidence of glaciation were neglected. Interglacial stages can be recognized on the basis of intercalations of well-sorted sediments, without glacigenic features (Dickins, 1985). Fossiliferous beds, or a transgression with abundant marine fauna between two discrete glacial members, may suggest important defrosting (González, 1990). Elsewhere I have commented on the chronology and durations of those glaciations (González, 1990). Ice sheets could spread over large areas, and occasionally glaciers may have behaved as temporary dams, actually isolating inland seas.