LATE DEVONIAN GLACIATION IN GONDWANA AND LAURENTIA AND ITS CONSEQUENCES

The Late Devonian glaciation event was first described by Caputo (1985). Continued work by various Brazilian authors demonstrated glacial deposits in the Solimoes, Amazonas, and Parnaiba basins. Later work showed that the glaciation affected Bolivia (Díaz-Martínez and Isaacson, 1994) and Peru (Carlotto et al., 2004). Newer work (e.g., Cunha, et al. 1994; Eira, et al., 1994; Goes and Feijo, 1994) presents evidence for Late Devonian diamictites and other glacial features in Africa. Recent data from the Appalachians (Pennsylvania and Maryland, U.S.A.) (Cecil, et al., 2004) show similar glacial features, whose stratigraphic position indicates a Late Devonian age. In South America, sedimentation took place in shallow-marine siliciclastic environments within two different geodynamic and palaeogeographic settings (Díaz-Martínez, 2004). To the west, Bolivian and Peruvian sequences were deposited in a retroarc foreland basin along the active margin of western Gondwana, with local tectonic instability and locally high sedimentation rates. Uplift along this orogen favored local glaciation and the development of icefields with valley glaciers that reached the marginal basin during a single event of late Famennian age. In contrast, Brazilian sequences were deposited in intracratonic basins, with more widespread glaciation and development of icecaps, and ice tongues reaching the interior basins during several events from late Frasnian to Tournaisian. Palynological dating of Devonian glacial marine deposits in Peru and Bolivia, both in outcrop (Altiplano, Eastern Cordillera and Subandean) and in subsurface (Madre de Dios, Chaco), indicate a late Famennian age (lepidophyta-pusillites zone) of the main glacial event in the region. Consequences of the glaciation include lacunae, phreatic zone carbonate brecciation (W Laurentia), termination of extensive Frasnian carbonate banks, iron oolites (North Africa), and extensive epeiric sea black shales with high TOC (Isaacson et al., 1999).