Clay minerals and gamma-ray spectrometry as paleoclimatic indicators in the gondwana’s sedimentary sequences, Santa Catarina, Brazil

Abstract

This work presents clay minerals data and gamma spectrometry to accesses the paleoclimatic signature during the depositional transition from Taciba to the Rio Bonito Formation in the eastern edge of the Paraná Basin. Detrital illite content (50 to 60%) and chemical index alteration indicates low-influence of chemical weathering. The eTh/K and eTh/eU ratios and detrital illite in the Rio Bonito Formation indicate a cold and dry climate during deposition. The contrast between the increase in eTh/K and eTh/eU ratios and the decrease in the illite content toward the top of the Rio Bonito Formation suggests progressively warmer and humid climatic conditions. The cycling in the eTh/K and eTh/eU ratios clearly indicate seasonal variations in temperature and leaching of K and eU.