Temporal relationship between cratonization and glaciation: The Vendian-early Cambrian glaciation in Western Gondwana
Abstract Cratonization has long been said to favour glaciation: cratons would be ideal cradles for the development of continental ice-caps. In Western Africa, the widespread continental glaciation, developed near the Proterozoic-Paleozoic boundary, can no longer be considered as Vendian. According to the recent discovery of an Early Cambrian microfauna in Eastern Senegal, it extends until Atdabanian time (530-520 Ma). The age of its beginning lacks in precision: it can be Vendian or Early Cambrian. In the Hoggar fold belt, it constitutes the lower part of molassic intermontane sequences where it is about 30–40 Ma younger than the Pan-African cratonization dated at 600 Ma. This extensive cratonization closed the old long-lived Pan-African-Brasiliano cycle (∼1000-600 Ma) and is responsible for the aggregation of West Gondwana. In the South American Paraguay belt, glacial sequences also postdate Brasiliano cratonization dated at 590 Ma. They are probably Vendian, overlain by an Ediacara-like fauna and slightly older than those of Western Africa. The glaciation was restricted to the shoulders of rifted basins initiating the young, short-lived Pan-African-Brasiliano cycle (600, or slightly younger, to 520 Ma). World distribution of continents indicate that the widespread Late Vendian (?)- Early Cambrian ice cap glaciation of West Africa developed at middle latitudes (50-30°), whereas the probably Vendian glaciation of the Paraguay belt, restricted to local highlands, occupied high to middle latitudes (60°). In Western Gondwana, glaciation and cratonization occurring near the Proterozoic-Cambrian boundary appear as distinct and temporary unrelated phenomena.