LATE DEVONIAN AND EARLY CARBONIFEROUS GLACIATIONS IN SOUTH AMERICA

Three well-demonstrated glacial episodes, plus a fourth questionable one, are recorded in Late Devonian – Early Carboniferous sections of South America, on the basis of varied evidence (paleontological, geochemical, sedimentological, and global eustasy).

The poorly documented glacial record concerns the Frasnian/Famennian boundary in the Parnaíba Basin of northeast Brazil. Here, the Pimenteira Formation, a Middle to Late Devonian marine rock unit mainly composed of dark grey shales and siltstones with subordinated sandstones, presents a distinctive sandstone interval at the Frasnian/Famennian boundary, in the subsurface of the basin, which suggests a brief regressive fluctuation within a dominantly transgressive section, due to a cooling event. In Bolivia, dropstones have been described from the Colpacucho Formation of late Frasnian – early Famennian age, which point out to a possible glacial origin for the same.

The second glacial episode, of latest Famennian age, is well documented in basins of Brazil, and also in Bolivia and Peru. Biostratigraphically, it corresponds to the LE and LN spore zones of Western Europe. In Bolivia, glacio-marine diamictites have been identified in the Cumaná Formation of late Famennian age.

The third episode is recorded in the subsurface of the Solimões Basin during the late middle to early late Tournaisian. The resulting diamictites are lithologically very similar to the end-Devonian ones, and often rest unconformably upon them.

The fourth glacial episode is of late Viséan age. Its deposits are currently identified in Parnaíba (Poti Formation), Amazonas (Faro Formation) and Solimões (Jandiatuba Formation) basins. Diamictites of the Faro and Jandiatuba Formations are restricted to the subsurface. In Bolivia, late Viséan tillites of the Ambo Group also display characteristic glacial features.

All these glaciogenic units are underlain by erosional unconformities associated with, abrupt sea-level falls and glacial abrasion. Indirect evidence of these Paleozoic glaciations is documented in Western Europe and the United States on the basis of geochemical, stratigraphic, sedimentological, paleontological and eustatic data.

Such indirect evidence of the Northern Hemisphere presents good correlation with the more obvious lithological evidence recorded in South America, and discussed in the present work.