Chapter 48 Neoproterozoic successions of the São Francisco Craton, Brazil: the Bambuí, Una, Vazante and Vaza Barris/Miaba groups and their glaciogenic deposits

Abstract

The Neoproterozoic successions of the São Francisco Craton are primarily represented by the Bambuí and Una groups, deposited in cratonic epicontinental basins, and by the Vazante and Vaza Barris/Miaba groups, which accumulated on passive margins on the edges of the craton. The epicontinental basins comprise three megasequences: glaciogenic, carbonate platform (marine) and dominantly continental siliciclastics. Possible correlative sequences are observed in the passive margin deposits. At least two major transgressive-regressive sea-level cycles occurred during the evolution of the carbonate megasequence, which lies above glaciomarine diamictites of probable early Cryogenian (i.e. Sturtian) age. C, O, Sr and S isotope trends from analyses of well-preserved samples, together with lithostratigraphic observations, provide reasonable correlations for most of the Neoproterozoic successions of the São Francisco Craton. The 87 Sr/ 86 Sr record of these successions, ranging from 0.70769 to 0.70780, supports the proposed correlation with the Bambuí, Una and Vaza/Barris successions, and with the basal units of the Vazante Group. In addition, C-isotope positive excursions ranging from þ8.7 to þ14‰ and negative excursions from -5.7 to -7‰ VPDB in the Bambuí, Una and Vaza-Barris successions provide key markers for correlations. The precise ages of the sedimentation in these successions remains a matter of debate, but organic shales of two units of the Vazante Group have been dated by Re-Os techniques in two different laboratories, both yielding Mesoproterozoic ages. The Neoproterozoic and Mesoproterozoic successions preserve significant glaciogenic deposits.

Facies analysis, sequence stratigraphy and chemostratigraphy of the Sete Lagoas Formation (Bambui Group), northern Minas Gerais State, Brazil: evidence of a cap carbonate deposited on the Januária basement high

“…C negative values, some of them concordantly superimposed on glaciogenic diamictites (Misi et al 2011;Caxito et al 2012;Paula-Santos et al 2015). Such deposits at the base of the Sete Lagoas Formation have been interpreted as cap carbonates (Misi 2001;Martins and Lemos 2007;Lima 2011;Misi et al 2011;Caxito et al 2012;Paula-Santos et al 2015;Kuchenbecker et al 2016).…”

“…Such deposits at the base of the Sete Lagoas Formation have been interpreted as cap carbonates (Misi 2001;Martins and Lemos 2007;Lima 2011;Misi et al 2011;Caxito et al 2012;Paula-Santos et al 2015;Kuchenbecker et al 2016). The Sete Lagoas cap carbonates have been related to the Sturtian glaciation (~740 Ma; Babinski et al 2007;Vieira et al 2007), Marinoan glaciation (~635 Ma, Caxito et al 2012), and Marinonan or younger glaciation (Lima 2011).…”

Fluoride Levels in the Groundwater and Prevalence of Dental Fluorosis in the Municipality of Santana, in Region Karstic of West Bahia, Brazil

“…The geology includes pelitic, calcareous, and dolomitic rocks of Neoproterozoic age belonging to the Bambuí Group [30]. In addition, there are pelitic rocks (siltstones, shales, argillites, and slates) with subordinate limestones.…”

Correlations of some Neoproterozoic carbonate-dominated successions in South America based on high-resolution chemostratigraphy

“…Although some authors consider that the sediments have accumulated in foreland basins during compressive tectonic events (e.g. glacial diamictites in the basal section (D'el Rey Silva 1999; Misi et al 2011). According to Misi et al (2007), an extensional stage related to the break-up of the Rodinia supercontinent (900 -600 Ma), responsible for the glaciogenic and marine carbonate mega-sequences, is partially co-incident with the Brasiliano-Pan African orogeny (650 -500 Ma), which is responsible for the molasse mega-sequence sedimentation at the upper section.…”