PALEOPRECIPITATION CHANGES BASED ON PALEOSOLS PROFILES OF THE MARÍLIA FORMATION (UPPER CRETACEOUS) IN THE EASTERN PORTION OF THE BAURU BASIN IN SOUTHEASTERN BRAZIL

Resumo

The Marília Formation is a Maastrichtian sequence of the Bauru Basin that crops out in the Southeastern Brazil. This formation consists of an illuvial deposits succession characterized by alternating sedimentary strata and paleosols. Pedogenic features related to climatic factors can be used as a tool for the interpretation of paleoenvironments. Through macro- and microscopic descriptions, mineralogical analysis and geochemical data, twenty paleosol sections were identified and characterized in the Marília Formation. The characterization of C, Ck, Bt, Btk and Gley horizons and the geochemical data allowed the identification of paleoclimatic factors influencing the formation of paleosols. Changes in the formation processes of these paleosols were mainly triggered by moisture variations. Paleoprecipitation estimates (MAP) obtained from CIA-K values in Bt and Btk horizons indicate that the precipitation rates varied from 20 to 1000 mm/year. These contrasting climatic conditions caused the overlap of distinct paleosol profiles, suggesting oscillation between arid to semi-arid conditions. The results from this work contribute to a better understanding of the Upper Cretaceous paleoclimatic in the Southeastern Brazil.