Post-Marinoan paleoredox and paleoproductivity record in Puga cap carbonate: Implication for coastal life colonization at the Amazon Craton marginal Sea

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2025-01, Vol.657, p.112600, Article 112600
• Main Authors: dos Santos, Renan F., Sansjofre, Pierre, Nogueira, Afonso C.R., Hohl, Simon V., Bom, Marlone H.H., Brito, Ailton S., Callefo, Flavia, Lalonde, Stefan V.
• Format: Article
• Language: English
• Subjects: Amazonia; Biogeochemical zoning; Brazil; Cap dolostone; carbonates; dolomitic limestone; Environmental control; glaciation; marine environment; Microbialites; palaeogeography; paleoceanography; paleoclimatology; paleoecology; primary productivity; sea level; Trace elements
• ISSN: 0031-0182
• DOI: 10.1016/j.palaeo.2024.112600

The geochemical signatures in cap carbonate successions are critical records of paleoceanographic conditions following Snowball Earth events. These deposits offer insight into the shifts in redox conditions and the re-establishment of biogeochemical cycles during postglacial periods, providing a window into the evolving marine environments and potential drivers of early oxygenation. To track redox changes during this transition, we present improved high-resolution analyses of redox proxies across Puga cap carbonate (∼ 635 Ma) on the Southern Amazon Craton, Brazil, allowing for the identification of temporal redox transitions during the post-Marinoan transgression. The depletion of trace elements, particularly redox-sensitive elements (RSEs), such as Mo, U, and V in microbialites formed in basal cap dolostone, was deposited under oxic conditions. Following the initial melting of Marinoan glaciers, microbial mats flourished and grew in a semi-restricted shallow marine environment in the coastal paleoenvironment along the Amazon cratonic margin, where nutrient-rich surface waters fueled primary productivity. In contrast, the increase in RSEs in upper wave-dominated dolostone facies indicates predominantly dysoxic conditions in continuous sea level rise, resulting in the drowning of these early microbial environments and the precipitation of cap limestones. The sequential oxic-dysoxic redox marks the transition from shallow sea to deepening CaCO3-oversaturated platform conditions. These results demonstrate an unequivocal synchronous relationship between the initial oxygenation of the Amazon margin and the local microbial mat flourishment shortly after the Marinoan glaciation. •Complex environmental and biogeochemical cycles interplay in post-Marinoan (∼635 Ma).•Climatic extreme geological scenarios shed critical light on the life proliferation.•Microbial mat flourishment occurs under oxic conditions in coastal environments.•Microbial communities could be self-sufficient under shallow marine conditions.•Sequential redox transitions from oxic to dysoxic conditions occur in response topaleoceanographic changes