Radioactivity and radiogenic heat production in the sediments of the São Francisco sedimentary basin, Central Brazil

Uranium, thorium and potassium measurements, followed by radioactive heat generation calculations were made in Bambuí Group neoproterozoic sedimentary rocks from the São Francisco Basin, Brazil. The measurements were made in drilling cuttings recovered from a deep well drilled near the city of Pirapora, central Minas Gerais State, and in Bambuí Group outcrop samples from Minas Gerais. The obtained results allowed the construction of vertical profiles of concentration of the heat generating elements, of the heat generation rate and of the U/Th, U/K and Th/K ratios in these sediments. U, Th and K concentrations reflect mainly the lithology, whereas the variability of U/Th, U/K and Th/K, besides the lithology, also seem to indicate variations in sedimentation conditions in part of the Bambuí Group Formations sampled by the deep well. The Bambuí Group contribution to the local heat flow density is <0.37 mW/m2.