Late Pennsylvanian aridification in Gondwana mid-latitudes contemporaneous to high-latitudes ice cap expansion, upper Piauí Formation, Brazil

Abstract

The Pennsylvanian Epoch was marked by a well-known glaciation period documented in several basins across the Gondwana. However, stratigraphic data from the Parnaíba Basin suggest that drier climate conditions dominated mid-paleolatitudes simultaneously to the glaciation. To investigate the possible time equivalence and the causes of aridification in mid-paleolatitudes, high-resolution stratigraphic analysis of the upper Piauí Formation were conducted in the eastern margin of the Parnaíba Basin. As a result, three stratigraphic intervals separated by key stratigraphic surfaces were identified: The first stratigraphic interval is dominantly composed of fluvial deposits progressively overlain by eolian facies; the second stratigraphic unit is essentially composed of lacustrine deposits and represent a regional flooding related to a period of lake expansion and finally, the third stratigraphic unit is characterized by three eolian genetic units and depicts cyclic expansion and contraction of a dune field. The overall vertical stratigraphic succession represents a progressive change from original fluvial sedimentation to essentially eolian accumulation and constitutes a drying upward trend that reflects an increasing aridification in the Parnaíba Basin during the Late Pennsylvanian age. The detailed analysis of the paleoclimatic conditions and the atmospheric circulation during the Late Pennsylvanian Epoch evidenced that the waning and waxing of the ice sheets controlled the development, expansion and contraction of the upper Piauí Formation dune-field.