Anoxygenic photosynthesis linked to Neoarchean iron formations in Carajas (Brazil)

Author(s)

Rego, Eric Siciliano ^{[1, 2, 3]} ; Busigny, Vincent ^[2] ; Lalonde, Stefan V. ^[4] ; Philippot, Pascal ^{[5, 2, 3]} ; Bouyon, Amaury ^[3] ; Rossignol, Camille ^{[5, 2]} ; Babinski, Marly ^[1] ; de Cassia Zapparoli, Adriana ^[6]

Affiliation

^[1] Univ Sao Paulo, Inst Geociencias, Rua Lago 562, BR-05508080 Sao Paulo - Brazil

^[2] Univ Paris, CNRS, Inst Phys Globe Paris, Paris 05 - France

^[3] Univ Antilles, Univ Montpellier, CNRS, Geosci Montpellier, F-34095 Montpellier - France

^[4] Univ Bretagne Occidentale, CNRS, Inst Univ Europeen Mer, Plouzane - France

^[5] Univ Sao Paulo, Dept Geofis, Inst Astron Geofis & Ciencias Atmosfer, Sao Paulo - Brazil

^[6] Vale SA, CTF, Nova Lima - Brazil

• Document type: Journal article
• Source: Geobiology; v. 19, n. 4, p. 326-341, JUL 2021.
• Web of Science Citations: 0

Abstract

Microbial activity is often invoked as a direct or indirect contributor to the precipitation of ancient chemical sedimentary rocks such as Precambrian iron formations (IFs). Determining a specific metabolic pathway from the geological record remains a challenge, however, due to a lack of constraints on the initial conditions and microbially induced redox reactions involved in the formation of iron oxides. Thus, there is ongoing debate concerning the role of photoferrotrophy, that is the process by which inorganic carbon is fixed into organic matter using light as an energy source and Fe(II) as an electron donor, in the deposition of IFs. Here, we examine similar to 2.74-Ga-old Neoarchean IFs and associated carbonates from the Carajas Mineral Province, Brazil, to reconstruct redox conditions and to infer the oxidizing mechanism that allowed one of the world's largest iron deposits to form. The absence of cerium (Ce) anomalies reveals that conditions were pervasively anoxic during IF deposition, while unprecedented europium (Eu) anomalies imply that Fe was supplied by intense hydrothermal activity. A positive and homogeneous Fe isotopic signal in space and time in these IFs indicates a low degree of partial oxidation of Fe(II), which, combined with the presence of C-13-depleted organic matter, points to a photoautotrophic metabolic driver. Collectively, our results argue in favor of reducing conditions during IF deposition and suggest anoxygenic photosynthesis as the most plausible mechanism responsible for Fe oxidation in the Carajas Basin. (AU)

• FAPESP's process: 18/02645-2 - Chronostratigraphy and isotopic tracing of the Paleoproterozoic Minas Supergroup
• Grantee: Camille Yann Rossignol
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 19/16271-0 - Element and isotope geochemistry from iron formations, carbonates and black shales: new insights into paleoredox conditions during the Neoarchean, Paleo- and Neoproterozoic in Brazil
• Grantee: Eric Siciliano Rego
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 15/16235-2 - The co-evolution of life and oxygen on early Earth: a South American perspective
• Grantee: Pascal Andre Marie Philippot
• Support Opportunities: Research Projects - SPEC Program