The geochemical characteristics of the Parana River suspended sediment load: an initial assessment

Most water in the Parana River drainage basin is supplied by the tropical Upper Parana (over 60% of the total annual water discharge, 550 km(3)). The total suspended solids (TSS) load (c. 80 X 10(6) t year(-1)), however, is essentially furnished (50-70%) by the mountainous, and and mostly sediment-mantled upper Bermejo River drainage basin. This characteristic suggests that the Parana River solid load (TSS, 600 km upstream from the mouth) is largely recycled sedimentary material, whose discharge-weighted mean chemical index of alteration is c. 71. The extended UCC-normalized multi-elemental diagrams are similar to those of other world rivers. Nevertheless, the detailed inspection of UCC-normalized rare earth element (REE) 'spidergrams' reveals a lithological source for the Parana River TSS that might be compatible with either tholeiitic flood basalts (widespread in the upper drainage) or with young Andean intermediate volcanic rocks. In view of the Bermejo River's dominant role as a sediment contributor, we feel that the signature preserved in the Parana's TSS is the latter. Conversely, the Uruguay River TSS REE signature is certainly determined by the extensive weathering products of Jurassic-Cretaceous tholeiitic basalts. Copyright (C) 2003 John Wiley Sons, Ltd.