Paleoproterozoic manganese oxide precipitation in oxic seawater surface and reductive enrichment in anoxic seafloor

Accelerated precipitation of Mn-rich rocks in the early Paleoproterozoic ocean is considered to reflect irreversible rise oxygen atmosphere during Great Oxidation Event (GOE), 2.501–2.220 billion years ago. But conditions, pathways, mechanisms, and linkages redox, broadly remain unresolved. The Lagoa do Riacho Mn deposit Borborema Province, northeastern Brazil, Ceará state, consists mainly manganese-rich manganese-poor silicates deposited GOE epoch. Negative Ce anomalies point scavenging 3+ onto Mn-oxyhydroxide reactive surfaces oxygenated surface waters. In contrast, samples with positive anomalies, predominantly associated silicates, indicate a reductive dissolution Mn-oxyhydroxides across redoxcline, enriching anoxic bottom water 2+ . A paleoredox reconstruction based on couple Mn, Mo, U systematics supports existence proposed Mn-oxide redox shuttle that enriched sediment pile precipitated from shallow This study uncovers unique pathway mineralization involving transfer oxides an upper reservoir deep silicate was subsequently metamorphosed. oxide sink switch mechanism different commonly reported diagenetic carbonate Paleoproterozoic. • manganese-bearing Brazil. Positive redox-stratified column. Reductive take place redoxcline. Paleoredox proxies oxic waters sediment-water interface.