C, O, and Sr isotopic variations in Neoproterozoic-Cambrian carbonate rocks from Sete Lagoas Formation (Bambuí Group), in the Southern São Francisco Basin, Brazil

Abstract

High-resolution chemostratigraphic data of carbonates from the Sete Lagoas Formation (Bambuí Group) show large variations on the C, O, and Sr isotope compositions. Impure limestones at the base show primal δ 13 C values between -1.0 and 0‰, and δ 18 O values between -12.0 and -8.0‰. However, some dolostones demonstrate δ 13 C values varying from +2.8 to -6.8‰, highly radiogenic 87 Sr/ 86 Sr ratios (>0.7111), and low Sr concentrations (<350 ppm) related to post-depositional processes. In contrast, pure limestones at the top show very positive δ 13 C values between +8.3 and +12.8‰, δ 18 O values between -10.0 to -6.0‰, and 87 Sr/ 86 Sr ratios from 0.7073 to 0.7086, with high Sr concentrations (>900 ppm). They are linked to depositional controls on the carbonate platform, such as fluvial and/or submarine water influx, in which carbonates deposited on the proximal sector exhibit significant Sr isotopic variations and those on the distal sector were not subject to such controls, resulting in very homogeneous Sr isotope profiles. However, 87 Sr/ 86 Sr ratios of the distal carbonates are less radiogenic than carbonates expected for late Ediacaran (~0.7085). This discrepancy suggests a restricted marine basin without Sr isotopic homogenization with contemporary oceans and, in this case, global correlations based on Sr isotope stratigraphy are not reliable. KEYWORDS:Isotopes; Carbonates; Bambuí Group; Ediacaran. RESUMO: Dados quimioestratigráficos de alta resolução em carbonatos da Formação Sete Lagoas (Grupo Bambuí) apresentam grandes variações nas composições isotópicas de C, O e Sr. Os calcários impuros na base da unidade mostram valores primários de

Sedimentary provenance in the southern sector of the São Francisco Basin, SE Brazil

“…Ten samples from the Sete Lagoas Formation were collected, covering the three Chemostratigraphic Intervals (CI) proposed by Paula-Santos et al (2017). One marl sample (P6, Tab.…”

“…Additionally, Paula-Santos et al (2017) suggested that the initial increase in 87 Sr/ 86 Sr isotope ratios from 0.7074 to 0.7082 in the cap carbonate ) is not a peak, but rather, they stabilize close to 0.7085 in the CI-2. This also suggests that there is no major hiatus or a long-lived sedimentation history between the cap carbonates and the remaining lower Sete Lagoas Formation.…”

Quimioestratigrafia isotópica (C, O, Sr) de alta resolução dos carbonatos da Formação Sete Lagoas, Grupo Bambuí, na região sudoeste da Bacia do São Francisco

“…Os estudos isotópicos de Sr têm sido menos frequentes, porém o entendimento deste sistema isotópico evoluiu bastante com as pesquisas da última década (e.g. Caxito et al, 2012;Paula-Santos et al, 2015Kuchenbecker et al, 2016b;Guacaneme et al, 2017). A Formação Sete Lagoas 13 C bastante característico e com expressão regional (Caetano-Filho et al, 2019).…”

“…Francisco (e.g. Alvarenga et al, 2007Alvarenga et al, , 2014Babinski et al, 2007;Misi et al, 2007;Caxito et al, , 2018Paula-Santos et al, 2015Kuchenbecker et al, 2016b;Guacaneme et al, 2017). Para a capa carbonática, um aumento nas razões 87 Sr/ 86 Sr de 0,7074 para 0,7082 é reportada por Babinski et al (2007).…”

“…Para a capa carbonática, um aumento nas razões 87 Sr/ 86 Sr de 0,7074 para 0,7082 é reportada por Babinski et al (2007). Acima dos carbonatos de capa são apresentadas razões 87 Sr/ 86 Sr com alta oscilação entre 0,7073 e 0,7085 (Alvarenga et al, 2007(Alvarenga et al, , 2014Kuchenbecker, 2011;Caxito et al, 2012Caxito et al, , 2018Paula-Santos et al, 2015Guacaneme et al, 2017).…”