The Carrancas Formation, Bambuí Group: A record of pre-Marinoan sedimentation on the southern São Francisco craton, Brazil. (November 2016)

• Record Type: Journal Article
• Authors: Uhlein, Gabriel J.; Uhlein, Alexandre; Halverson, Galen P.; Stevenson, Ross; Caxito, Fabrício A.; Cox, Grant M.; Carvalho, Jorge F.M.G.
• Is Part Of: Journal of South American earth sciences. Volume 71(2016:Nov.)
• Page Start: 1
• Page End: 16
• Publication Date: 2016-11
• Subjects: Neoproterozoic -- Marinoan glaciation -- Isotope stratigraphy -- Keele peak -- São Francisco craton -- Bambuí Group; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2016.06.009
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: The Carrancas Formation outcrops in east-central Brazil on the southern margin of the São Francisco craton where it comprises the base of the late Neoproterozoic Bambuí Group. It is overlain by the basal Ediacaran cap carbonate Sete Lagoas Formation and was for a long time considered to be glacially influenced and correlative with the glaciogenic Jequitaí Formation. New stratigraphic, isotopic and geochronologic data imply that the Carrancas Formation was instead formed by the shedding of debris from basement highs uplifted during an episode of minor continental rifting. Reddish dolostones in the upper Carrancas Formation have δ 13 C values ranging from +7.1 to +9.6‰, which is a unique C isotopic composition for the lowermost Bambuí Group but similar to values found in the Tijucuçu sequence, a pre-glacial unit in the Araçuaí fold belt on the eastern margin of the São Francisco craton. The stratigraphic position below basal Ediacaran cap carbonates and the highly positive δ 13 C values together indicate a Cryogenian interglacial age for the Carrancas Formation, with the high δ 13 C values representing the so-called Keele peak, which precedes the pre-Marinoan Trezona negative δ 13 C excursion in other well characterized Cryogenian sequences. Hence, The Carrancas Formation pre-dates de Marinoan Jequitaí Formation and represents an interval of Cryogenian stratigraphy not previously known to occur on the southern margin of São Francicso craton. Documentation of Cryogenian interglacial strata on the São Francisco craton reinforces recent revisions to the age of Bambuí Group strata and has implications for the development of the Bambuí basin. Graphical abstract: Highlights: The Carrancas Formation (base of the Bambui basin) was deposited in a rift basin. A pre-Marinoan sedimentation is suggested for the Carrancas Formation. Carbon isotopic chemostratigraphy imply correlation with the global Keele peak. The Carrancas Formation correlates with the Tijucuçu sequence, in the Aracuaí belt. Cryogenian interglacial strata was not previously known on the São Francicso craton.