Quaternary of the Pantanal, west-central Brazil

Abstract

The Pantanal is a tectonic depression located at the left margin of the Upper Paraguay River. The Paraguay is the trunk river of an alluvial depositional tract composed by several large marginal alluvial fans, the Taquari fan being the largest one. The present landscape is a complex tropical wetland characterized by month-long floods every year, with geomorphic features derived from the present conditions and others inherited from successive Pleistocene and Holocene climates. Some areas containing ponds are landscape relicts generated by eolian deflation during the Last Glacial Maximum. Many ponds, closed depressions isolated from the superficial waters by vegetated crescent ridges of fine sands, were interpreted as salt pans bordered by lunette sand dunes. Initiation of the modern wetland has occurred during the Pleistocene/Holocene transition, with the change to a more humid climate and the individualization of lacustrine systems. Active tectonics has been playing an important role in the development of the Pantanal landscape. Nowadays, the Paraguay River meanders in a large flood plain with extensive swamp surfaces, being structurally constrained by faults in the west border of the basin. Sedimentation within the Pantanal wetland is also affected by tectonic activity, especially along faults associated with the Transbrasiliano Lineament.