Variações dos isótopos de C e Sr em carbonatos pré e pós-glaciação Jequitaí (Esturtiano) na região de Bezerra-Formosa, Goiás

Abstract

Carbonate rocks of the upper Paranoá Group and lower Bambuí Group (Sete Lagoas Formation) have been founded at the occidental border of the São Francisco craton. These units have been separated by the Sturtian glaciation, identified by Jequitaí Formation, but in some localities the glacial record is absent and is difficult to separate these two carbonates units. In this paper two sections with a good stratigraphic control have been chosen to find C, O and Sr isotopic values to have tools for the correlations. Carbonates of the Paranoá Group present a trend of positive δ 13 C PDB varying between +0.8 e +2.7‰, of δ 18 O PDB varying between -9.0 e -4.7‰ and 87 Sr/ 86 Sr ranging from 0.7063 to 0.7068. The diamictite sample of Jequitaí Formation has δ 13 C PDB values of -1.8‰ and δ 18 O PDB values of -5.1‰. The cap dolomites of the Sete Lagoas Formation are associated with an extremely negative δ 13 C PDB values between -6.0 e -3.2‰, δ 18 O PDB values between -9.1 e -5.3‰ and high 87 Sr/ 86 Sr ratios suggesting a radiogenic Sr isotope anomaly. Limestone and muddy-limestone above the cap dolomite still starts with extremely negative δ 13 C PDB values (-6.0‰) and are followed by an upward trend of increasing carbon isotope values up to +9.2‰. In the same interval the δ 18 O PDB values ranging from -10.1‰ at the base to -5.5‰ in direction to the top of formation and primary 87 Sr/ 86 Sr ratios between 0.70745 and 0.70758. The Carbon and Sr isotope data presented here reveal significant differences between carbonates from the Paranoá Group and the Bambuí Group. These data developed here provides the framework for a new regional isotopic correlation model to the carbonates units of the Paranoá and Bambuí groups.