Carbon isotopes of Mesoproterozoic–Neoproterozoic sequences from Southern São Francisco craton and Araçuaí Belt, Brazil: Paleographic implications

Abstract: This paper addresses the carbon isotope variations observed on Mesoproterozoic and Neoproterozoic carbonates from the southeastern part of the São Francisco craton and Araçuaí Belt, Brazil. Carbonates were collected across sections of the Mesoproterozoic Espinhaço Supergroup (Rio Pardo Grande Formation) and of the Neoproterozoic units of the São Francisco basin, including: (i) dolomites and marls of the Macaúbas Group (Domingas Formation); (ii) dolomite pebbles and carbonatic matrix of the diamictites of the Jequitaí Formation; (iii) limestones of the overlying Bambuí Group. Limestones of the Espinhaço Supergroup present a flat trend of positive δ13CPDB values (varying between +1 and +2‰), while samples of the Macaúbas Group present an upward trend of decreasing carbon isotopic values (from +0.7 to -4.0‰). The lower δ13CPDB values of this latter unit were obtained on the upper part of the section. Dolostone pebbles and carbonates in the matrix of the diamictite also present negative δ13CPDB values (-3.1 and -0.6‰). Except for carbonatic pelites placed above the diamictites, that present δ13CPDB of +7.7‰, limestone samples of all the sections of the Bambuí Group have δ13CPDB values above +8‰. The data presented here reveal significant differences between carbonates from the Espinhaço and Macaúbas Groups, indicating that this latter unit may be correlated with the diamictites from the Jequitaí Formation, as already suggested by previous stratigraphic studies. The data also reveal the absence of the low positive δ13CPDB carbonates (below +3‰) frequently present at the base of the Bambuí Group, thus suggesting that the deposition of this unit in the Serra do Cabral and Jequitaí areas took place after the regional positive δ13CPDB excursion observed in other parts of the basin. Hence, it is proposed that these areas were paleo-highs during the deposition of the lower portion of the Bambuí Group sediments. [Copyright &y& Elsevier]