Late Devonian glaciation in South America

Abstract

An ice age in Famennian (Late Devonian) time is documented by the presence of diamictites with striated, faceted and polished pebbles; rhythmites with dropstones; erratic boulders; and striated pavements and deformed sandstones. The glacigenic beds occur in three huge intracratonic basins (Solimões, Amazonas and Parnaìba) and in one pericratonic basin (Acre) in northern Brazil. Other possible Late Devonian diamictites may occur elsewhere in Brazil and Africa which, if confirmed, would extend considerably the area affected by this glacial age. The onset of the Late Devonian glaciation caused a global narrowing of the warm climatic belts, sharp regression, increased clastic sedimentation, massive biotic extinction, reduced biochemical deposition and unconformities. This resulted in important facies changes in the world geological record. Ice centers moved from northern Africa to southwestern South America from Late Ordovician to Early Silurian time. From Mid-Silurian to early Late Devonian time no record of glaciation is known. In late Late Devonian time intermittent glaciation began again in central South America and, from late Late Devonian to early Late Permian time, ice centers migrated towards Antarctica across South America and South Africa. The Devonian and Ordovician-Silurian glaciations together with the better known Permo-Carboniferous glaciations may all have primarily resulted from the shifting position of the Gondwana continent with respect to the South Pole.