Facies, Facies Association and Depositional Model of Eolian Sandstones - Botucatu Formation (Lower Cretaceous) in Southern Santa Catarina State, Brazil

Abstract

Investigations of eolian deposits of Botucatu Formation situated at the southern portion of Santa Catarina State allowed the detailed facies characterization of the unit. In this area, the Botucatu Formation is thicker than adjacent areas, with packages that vary between 80 and 200 meters thick. The lower contact is an unconformity that removed deposits of the Rio do Rasto Formation (Permian). The upper contact is concordant with the basalts of the Serra Geral Formation. It is possible to individualize two litofacies: fine to coarse-grained sandstone with planar large scale cross stratification (ACGP) and fine to medium-grained sandstone with concave up medium scale cross stratification (ACMP). These litofacies compose only one facies association that consists of ACGP facies sets and locally by ACMP facies grouped sets. These deposits can be interpreted as resulting of simple crescentic dunes migration with straight to slightly sinuous crest line that locally develops secondary crescentic dunes in frontal face. The absence of wet interdune deposits led to the interpretation that the Botucatu Formation is the record of a dry eolian system. The thick accumulation of eolian dunes and wind pattern inflection along a preferential direction allowed to infer that the analyzed area was in the domain of a topographically depressed region, controlled by NW-SE faulting system related to the initial break up of the Gondwanaland.