Late Proterozoic glaciation in central-eastern Brazil: Synthesis and model

Abstract

In the surroundings of the Middle Proterozoic São Francisco Craton of central-eastern Brazil, numerous traces of an ancient glaciation can be found. Almost all criterua necessary to prove an ancient glaciation occur, including scratched and facetted pebbles, a striated surface, quarrying, outwash plains, eskers, varvites, dropstones, “décollement” structures etc. Poorly sorted tillites with varying pebble composition are widely distributed. Continental tillites and glaciomarine sequences interfinger in the east and southeast of the craton. Traces of ice movement suggest flow directions of the ice towards the east and the southeast of the craton. At the coast, the wet-base glaciers passed over to floating shelf ice. In the northeast, glaciers also came from the Serrinha Craton in northeastern Bahia. The glaciation covered an area of at least 1300 × 700 km. The sequences containing traces of glaciation discordantly overlie Archean to Middle Proterozoic rocks. They in turn are overlain by Late Proterozoic calcareous and psammopelitic sediments of the Bambuí Group. Present data indicate that glaciation took place around 1000 Ma ago.