Carbon isotope variations of high magnitude recorded in carbonate rocks from the Stenian-Tonian Lajeado Group, Southeast Brazil

Author(s)

Paula-Santos, Gustavo Macedo ^{[1, 2, 3]} ; da Cruz Campanha, Ginaldo Ademar ^[4] ; Faleiros, Frederico Meira ^[4] ; Bezerra Maia Hollanda, Maria Helena ^[4] ; de Oliveira Rodrigues, Sergio Wilians ^[5]

Affiliation

^[1] Univ Bremen, MARUM Ctr Marine Environm Sci, Leobener Str 8, D-28359 Bremen - Germany

^[2] Univ Bremen, Fac Geosci, Leobener Str 8, D-28359 Bremen - Germany

^[3] Univ Estadual Campinas, Inst Geociencias, Rua Carlos Gomes 250, BR-13083855 Campinas - Brazil

^[4] Univ Sao Paulo, Inst Geociencias, Rua Lago 562, BR-05508080 Sao Paulo - Brazil

^[5] Univ Fed Goias, Fac Ciencias & Tecnol, Rua Mucuri, BR-74968755 Aparecida De Goias - Brazil

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 109, AUG 2021.
• Web of Science Citations: 0

Abstract

The Lajeado Group is a Stenian-Tonian metasedimentary unit comprising a thick carbonate succession that was involved in the Brasiliano - Pan-African Ribeira orogenesis in Southeast Brazil. The carbonate rocks record significant carbon isotope variations, which provide further information about the Mesoproterozoic Earth system. The delta 13C values obtained along a composite vertical section vary between -5 and +5%o with two negative isotope excursions with magnitudes higher than 6%o. The coincidence between the isotopic trend of the Lajeado carbonate succession with equivalent units studied worldwide suggests that the deposition of the lower and middle parts of the unit may have occurred at 1.2-1.1 Ga, which is in agreement with recently published geochronological data. Despite the similarities, the Lajeado Group displays larger carbon isotope variations and negative isotope excursions of higher magnitudes when compared to coeval marine settings. We argue that the basin conditions may have been more favourable to build up large particulate (POC) and dissolved organic carbon (DOC) reservoirs. When oxidized they significantly impacted the dissolved inorganic carbon (DIC) pool, causing the negative excursions. If our scenario holds, the Lajeado Group may be considered an example of record of fluctuations in atmospheric pO2 levels and the oxidation state of the planet during the late Mesoproterozoic. (AU)

• FAPESP's process: 17/00399-1 - Chemical weathering and nutrient input into late Ediacaran ocean and their relationship to life diversification
• Grantee: Gustavo Macedo de Paula Santos
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/10012-0 - Fluid flow, deformation and tectonic significance of regional shear zones from the southern Ribeira Belt
• Grantee: Frederico Meira Faleiros
• Support Opportunities: Regular Research Grants