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Global or regional? Constraining the origins of the middle Bambui carbon cycle anomaly in Brazil
Cui, H.; Warren, L.V.; Uhlein, G.J.; Okubo, J.; Liu, X.-M.; Plummer, R.E.; Baele, J.-M.; Goderis, S.; Claeys, P.; Li, F. (2020). Global or regional? Constraining the origins of the middle Bambui carbon cycle anomaly in Brazil. Precambr. Res. 348: 105861. https://hdl.handle.net/10.1016/j.precamres.2020.105861
In: Precambrian research. ELSEVIER SCIENCE BV: Amsterdam; London; New York; Oxford; Tokyo. ISSN 0301-9268; e-ISSN 1872-7433
Peer reviewed article  
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Author keywords
    Middle Bambuf Excursion (MIRE); Carbon cycle; Sulfur cycle;Neoproterozoic; Chemostratigraphy; Biogeochemistry; Methanogenesis; Diagenesis; Geobiology; Ediacaran-Cambrian transition
Auteurs  Top 
  • Cui, H.
  • Warren, L.V.
  • Uhlein, G.J.
  • Okubo, J.
  • Liu, X.-M.
  • Plummer, R.E.
  • Baele, J.-M.
  • Goderis, S.
  • Claeys, P.
  • Li, F.
Abstract
    The Ediacaran-Cambrian Bambuí Group in Brazil records an anomalously positive excursion in carbonate carbon isotopes (d13Ccarb) with a sustained plateau of ca. +15‰ (aka the Middle Bambuí Excursion–MIBE). Considering that the d13Ccarb signals in Ediacaran-Cambrian seawaters do not typically exceed +6‰, the MIBE therefore represents a profound carbon cycle anomaly in Earth’s history. Although intensive studies have been done on the Bambuí 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 Jacaré Formation) and the recovery part (i.e., lower Serra da Saudade Formation) of the MIBE. Chemostratigraphic profiles reveal remarkably different values in d13Ccarb, d13Corg, d18Ocarb, and d34Spyrite between these two studied MIBE intervals. The new data show that the plateau of the MIBE is characterized by coupled higher d13Ccarb, higher d13Corg, and higher d34Spyrite 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 d13Ccarb 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.
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STARDUST II is a project funded by the INTERREG III A programme (France/Walloon Region/Flanders French-Flemish subprogramme) of the European Community's Regional Development Fund.
Hosted by the Flanders Marine Institute (VLIZ)