Paleo and present-day chemical weathering in lacustrine and riverine sediments in Northern Patagonia, Argentina

Neutron activation analysis was used to study the abundance, distribution and fraction of REE (Rare Earth Elements) and diagnostic elements (Th, Co, Cr, Sc, Rb, Sr) in sediments from Mascardi lake and Upper Manso river. The local weathering patterns of this watershed show a strong influence of volcanic rocks with a selective mobilization of the more soluble elements. These patterns are very similar to those observed in a sedimentary lacustrine core from Mascardi lake. Paleolimnological record indicates a change in local fluxes of water and sediments, and an increase in organic matter content since the last full-glacial maximum. However, the chemical composition of the sedimentary inputs has not changed significantly during the last 14000 years. Our data support the hypothesis that present-day and Holocene chemical weathering have similar characteristics. All of the above conclusions are based on geochemical parameters only. (author)