Global or regional? Constraining the origins of the middle Bambui carbon cycle anomaly in Brazil

Author(s)

Cui, Huan ^{[1, 2]} ; Warren, Lucas Verissimo ^[3] ; Uhlein, Gabriel J. ^[4] ; Okubo, Juliana ^[3] ; Liu, Xiao-Ming ^[5] ; Plummer, Rebecca E. ^[6] ; Baele, Jean-Marc ^[7] ; Goderis, Steven ^{[1, 2]} ; Claeys, Philippe ^{[1, 2]} ; Li, Fei ^[8]

Affiliation

^[1] Vrije Univ Brussel, Analyt Environm & Geochem Grp, Brussels - Belgium

^[2] ET HOME Evolut & Tracers Habitabil Mars & Earth A, Brussels - Belgium

^[3] Sao Paulo State Univ Unesp, Inst Geosci & Exact Sci, Dept Geol, Rio Claro, SP - Brazil

^[4] Univ Fed Minas Gerais, Ctr Pesquisas Manoel Teixeira Costa, Inst Geociencias, BR-31270901 Belo Horizonte, MG - Brazil

^[5] Univ N Carolina, Dept Geol Sci, Chapel Hill, NC 27599 - USA

^[6] USDA, Hydrol & Remote Sensing Lab, Beltsville Agr Res Ctr, Beltsville, MD 20705 - USA

^[7] Univ Mons, Fac Engn, Dept Geol, Mons - Belgium

^[8] Southwest Petr Univ, Sch Geosci & Technol, State Key Lab Oil & Gas Reservoir Geol & Exploita, Chengdu 610500 - Peoples R China

• Document type: Journal article
• Source: Precambrian Research; v. 348, SEP 15 2020.
• Web of Science Citations: 0

Abstract

The Ediacaran-Cambrian Bambuf Group in Brazil records an anomalously positive excursion in carbonate carbon isotopes (delta C-13(carb)) with a sustained plateau of ca. + 15 parts per thousand (aka the Middle Bambuf Excursion-MIBE). Considering that the delta C-13(carb) signals in Ediacaran-Cambrian seawaters do not typically exceed + 6 parts per thousand, the MIBE therefore represents a profound carbon cycle anomaly in Earth's history. Although intensive studies have been done on the Bambui Group, origins of the MIBE remain enigmatic. In order to better constrain the biogeochemical carbon and sulfur cycles during the MIBE, high-resolution chemostratigraphic analysis was conducted for both the plateau (i.e., Lagoa do Jacare Formation) and the recovery part (i.e., lower Serra da Saudade Formation) of the MIBE. Chemostratigraphic profiles reveal remarkably different values in delta C-13(carb), delta C-13(org),delta C-13(carb), and delta S-34(pyrite) between these two studied MIBE intervals. The new data show that the plateau of the MIBE is characterized by coupled higher delta C-13(carb), higher delta C-13(org), and higher delta S-34(pyrite) signals compared with the recovery part of the MIBE. Based on multiple lines of sedimentological, geochemical, and model evidence, we propose that the possibilities of enhanced organic carbon burial and porewater methanogenesis are insufficient to explain the MIBE. Instead, local or regional controlling factors, including water-column methanogenesis, low-sulfate conditions, and enhanced carbonate recycling in a restricted basin may have played a role, independently or in unison, in generating this profound positive delta C-13(carb) excursion. Therefore, the MIBE may reflect a regional event, instead of a global carbon cycle anomaly. We caution against the use of the MIBE in chemostratigraphic correlations on a global scale or any other attempt to infer global carbon cycling at that time. The biogeochemical landscape of the late Ediacaran-Cambrian basins and ocean margins may be more heterogeneous than previously thought. (AU)

• FAPESP's process: 18/26230-6 - 10 million years that changed the planet: paleoenvironmental context of the evolution of the first animals with skeleton in the Terminal Ediacaran Period
• Grantee: Lucas Verissimo Warren
• Support Opportunities: Regular Research Grants