ESTRATIGRAFIA DO CRETÁCEO SUPERIOR DAS BACIAS DO SUDESTE DO CHACO E DO PARANÁ (“BACIA DO NORTE” – URUGUAI): IDADE MAASTRICHITIANA DO PROCESSO DE CALCRETIZAÇÃO

In the last 40 years, successive revisions have been introduced to the lithostratigraphy of the Late Cretaceous of the Norte Basin, whose record is formed by predominantly siliciclastic continental fossiliferous sedimentary rocks. A factor that contributed to the terminology proliferation was the misplaced importance attributed to the epigenetic processes and products (calcretes and ferricretes, occasionally fossiliferous) affecting those siliciclastic rocks. Based on field work and lithological logs from a number of key areas, the validity of the original stratigraphic column showing, from base to top, the Guichon, Mercedes, Asencio and Queguay formations is supported. For those particular units, the lithostratigraphic scope given by the original definitions is correct and, with minimum adjustments, they should be restored for their practical usefulness as geological mapping units. An evolutionary scheme for the Late Cretaceous of the Norte Basin is herein presented, with the aim of contributing to a greater understanding of the succession of sedimentary and epigenetic processes. A Maastrichtian age is proposed for the carbonatic cementation and/or substitution that affected the Mercedes and Asencio formations, thus originating the Queguay Formation, based on absolute age of the calcite cement (~ 72 Ma; U-Pb), paleontological data, and the correlation established with similar events recorded in the Marilia Formation in the Bauru Basin (Brazil).