No dia 19/03, às 16h, na Sala de reuniões do CPGeo, o Prof. Dr. Prof. Dr. William Gilhooly (Department of Earth Sciences- Indiana University) ministrará a palestra “Recognizing environmental redox change: examples from a modern lake and Archean Brazilian terranes“.
Talk description: Modern anoxic lakes are often used as analog systems for studying the chemical and biological processes thought operative in the Archean. Here, we present data from a lake located in the Pacific Northwest, US, that is currently anoxic and sulfidic (euxinic). However, iron and sulfur chemistry combined with molecular data from the sediments suggest the lake was not always sulfidic but rather iron rich (ferruginous). We use these same geochemical proxies to track environmental change in deep time. Our data from the 2.7 billion year (Ga) old Rio das Velhas greenstone belt, Brazil, indicates the basin underwent a progressive change from ferruginous, to euxinic, to oxic conditions within a relatively short time span. These observations indicate there was free dissolved oxygen in the Brazilian terrane prior to the Great Oxidation Event (2.4 Ga).