RADIOACTIVITY AND RADIOGENIC HEAT-PRODUCTION IN THE SEDIMENTS OF THE SAO-FRANCISCO SEDIMENTARY BASIN, CENTRAL BRAZIL

Uranium, thorium and potassium measurements, followed by radioactive h eat generation calculations were made in Bambui Group neoproterozoic s edimentary rocks from the Sao Francisco Basin, Brazil. The measurement s were made in drilling cuttings recovered from a deep well drilled ne ar the city of Pirapora, central Minas Gerais State, and in Bambui Gro up outcrop samples from Minas Gerais. The obtained results allowed the construction of vertical profiles of concentration of the heat genera ting 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 mainl y the lithology, whereas the variability of U/Th, U/K and Th/K, beside s the lithology, also seem to indicate variations in sedimentation con ditions in part of the Bambui Group Formations sampled by the deep wel l. The Bambui Group contribution to the local heat flow density is <0. 37 mW/m(2). (C) 1997 Elsevier Science Ltd.