Rapid bioproductivity recovery following the Marinoan glaciation: Evidence from Sr-Cr-Cd isotopes and trace elements in the Morraria do Sul cap dolostone, Brazil

Author(s)

Fernandes, Henrique Albuquerque ; Boggiania, Paulo Cesar ; Frederiksen, Jesper Allan ; Campos, Marcelo Da Roz ; Cardoso-Lucas, Vinicius ; Freitas, Bernardo Tavares ; Frei, Robert

• Document type: Journal article
• Source: CHEMICAL GEOLOGY; v. 673, p. 21-pg., 2024-12-07.

Abstract

Early Ediacaran cap dolostones are distinctive strata deposited directly above glaciogenic rocks from the Marinoan Glaciation (650-635 Ma), one of the most dramatic ice ages in Earth's history. These cap dolostones were rapidly deposited during global synchronous deglaciation, being a superb depositional window into the immediate glaciation aftermath and suitable for investigating the icehouse-hothouse transition in this period. However, some aspects of this transition are still unclear, such as the timing of primary productivity recovery. Aiming to explore this question, we present new sedimentological, trace element, and Sr-Cr-Cd isotope data for the Puga cap dolostone in the Southern Paraguay Belt (Brazil), here termed Morraria do Sul Formation. The cap dolostone overlies diamictites, siltstones with outsized clasts, and basement rocks. It is divided into a basal dolograinstone and an upper tubestone-microbialite succession, with abundant vertical tube-like structures. The diamictites and siltstones were formed in a glaciomarine setting, within the range of ice-rafted debris. The basal dolograinstone facies of the cap dolostone was formed under high-energy post-glacial conditions, and the overlying tubestonemicrobialite facies was deposited in a low-energy, well-lit environment. Rare earth elements and yttrium (REY) preserved the original seawater-like pattern, displaying true negative Ce anomalies down to 0.84, indicating oxygenated shallow waters. The cap dolostone displays relatively high 87 Sr/ 86 Sr ratios, up to 0.7123, above the assumed value for the Early Ediacaran seawater, suggesting the influence of meltwater plumes in a salinity- stratified setting. Authigenic Cr isotope values ( delta 53 Cr auth ) are within the range of Bulk Silicate Earth (BSE) to slightly positive in the basal dolograinstone and negatively fractionated below BSE values in the tubestonemicrobialite facies, implying that microbial-influenced Cr reduction progressively increased upwards, controlling the isotopic fractionation. A rise upwards in delta 114 Cd, from-0.11 to 0.17 parts per thousand, reveals a substantial increase in Cd-uptake by biomass, and maximum estimates for seawater delta 114 Cd show values within the range of present-day surface seawater. The data presented herein suggest that significant primary productivity recovery occurred in the immediate aftermath of the Marinoan Glaciation. This study also shows the efficiency of combined trace elements and Sr-Cr-Cd isotope analyses on reconstructing past seawater chemistry and productivity levels. (AU)

• FAPESP's process: 21/02628-3 - Investigation of oxygen levels in the Ediacaran through isotopic chemostratigraphy (C, Sr, Cr, Cd) of the Tamengo Formation-Corumbá Group
• Grantee: Henrique Albuquerque Fernandes
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• FAPESP's process: 20/16140-0 - Paleoproterozoic and Neoproterozoic phosphorite depositional systems in Brazil, genetic processes and application in agriculture
• Grantee: Paulo César Boggiani
• Support Opportunities: Regular Research Grants
• FAPESP's process: 23/02223-9 - Cr-Cd-Sr isotopes and trace elements in Ediacaran carbonates of the Corumbá and Nama groups (Brazil and Namibia): tracking atmospheric oxygenation and paleoproductivity
• Grantee: Henrique Albuquerque Fernandes
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)