Barros, Omar Neto Fernandes, et al. “Concept of Time: Relations Between Alteration Degrees and Chronosequence and the Geomorphological Surfaces”. Semina: Ciências Exatas E Tecnológicas, vol. 21, no. 4, Dec. 2004, pp. 67-76, doi:10.5433/1679-0375.2000v21n4p67.