Quaternary ironstones in the Xingu River, eastern Amazonia (Brazil)

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Freire, Marilia Prado ; Goes, Ana Maria ; Fairchild, Thomas Rich ; Gautheron, Cecile ; Parra, Mauricio ; Pupim, Fabiano Nascimento ; Bertassoli Junior, Dailson Jose ; de Sousa, Leandro Melo ; Hartmann, Gelvam Andre ; Pinna-Jamme, Rosella ; Sawakuchi, Andre Oliveira

• Document type: Journal article
• Source: Quaternary Research; v. 110, p. 14-pg., 2022-05-05.

Abstract

Using a multimethod approach, including polarized light microscopy (PLM), scanning electron microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS), SEM with mineral liberation analyzer (MLA), X-ray diffraction (XRD), and Raman spectroscopy, we examined sub-recent ferruginous crusts in the Xingu River in the Amazon Basin that have formed since the Early Pleistocene (<1.2 Ma), as indicated by (U-Th)/He dating of goethite. Although now preserved as goethite, the size and form of the smallest components of the ironstone (nanorods) and the nature of isomorphic substitution in the goethite point to very early transformation of the original precipitate, an unstable hydrous ferrous oxide (HFO) mineral, into goethite. The fine, multiply undulating laminae of the ironstone contain abundant filamentous microbial molds and casts that together support identification of the crusts as ferruginous microbialites and suggest a role of bioinduction/bioinfluence in ironstone precipitation, although inorganic precipitation is also evident. The Xingu Quaternary ironstones are the first evidence of ferruginous microbialite in a modern freshwater system in South America and may hold clues to the recent history of the Xingu River. (AU)

• FAPESP's process: 18/23899-2 - Trans-Amazon Drilling Project: origin and evolution of the forests, climate, and hydrology of the South American tropics
• Grantee: André Oliveira Sawakuchi
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 19/24349-9 - Assessing the effects of past and future climate change on Amazonian biodiversity (CLAMBIO)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: BIOTA-FAPESP Program - Regular Research Grants
• FAPESP's process: 19/24977-0 - Environmental signals recorded in modern sediments of tropical South American rivers
• Grantee: Dailson José Bertassoli Junior
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/15123-4 - Past perspectives on tipping elements of the climate system: the Amazon Rainforest and the Atlantic Meridional Overturning Circulation (PPTEAM)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: Research Grants - Research Program on Global Climate Change - Young Investigators - Phase 2
• FAPESP's process: 18/15613-1 - Topographic construction along the northeastern Andes and the origin of the Transcontinental Amazon Basin
• Grantee: Mauricio Parra Amézquita
• Support Opportunities: Research Grants - Young Investigators Grants - Phase 2
• FAPESP's process: 16/11141-2 - Hydrologic variability and sediment supply of the Xingu and Tapajós rivers: climate change and anthropogenic impacts in eastern Amazon rivers during Holocene
• Grantee: Dailson José Bertassoli Junior
• Support Opportunities: Scholarships in Brazil - Doctorate