O GRUPO CAIUÁ (Ks): REVISÃO ESTRATIGRÁFICA E CONTEXTO DEPOSICIONAL

Abstract

A stratigraphic review of the Late Cretaceous sediments deposited on the Paraná Flood volcanics is presented in this paper. The review is mainly based on studies developed by Fernandes (1992) in the northwest of the Paraná and on the westernmost part of São Paulo states. Stratigraphic and sedimentologic characteristics of the units of the Caiuá Group, as well as the depositional environments and its paleogeographic distribution in the southwest part of the Bauru Basin (a Late Cretaceous depression developed in the south-central part of the South American Platform by thermo-mechanical subsidence) are discussed. This inland basin preserved a single sequence, wich is mainly of quartz sandstones and sandy mudstones (red beds) - with locally associated volcanic rocks - encompassing several stratigraphic units known as Bauru Group. This suprabasaltic cover is composed of two synchronous groups: Caiuá (with the Goio Erê, Rio Paraná and Santo Anastácio formations), and Bauru (with the Marflia, Adamantina, Uberaba formations, and the Taiúva Analcimites).The Santo Anastácio Formation (SAP) is composed of very fine to fine quartz sandstones, that sometimes exhibits incipient planar parallel or low inclinated cross bedding. The Rio Paraná (RPF) and Goio Erê (GEF) formations are composed of fine from very fine quartz sandstones. They are differentiated by the geometry of the lithofacies, degree of maturity (textural and mineralogic), and geographic position in the basin. The RPF is characterized by large cross bedding sets and high textural and mineralogical maturity, whereas the GEF shows typical massive or small scale cross-bedding, and is composed of sandstones of low degree of maturity, with frequent carbonate cement and concretions. The sequence deposited under semi-arid paleoclimate in an asymmetric endorheic basin, with more desertic conditions towards its interior. The Caiuá Group comprises aeolian deposits of sand sea in an interior paleodesert of the basin. The Bauru Group comprises alluvial deposits, that includes marginal alluvial fans to distal facies accumulated on broad plains of braided streams with ephemeral alkaline water lakes. Keywords: