CONTRIBUIÇÃO AO ESTUDO DA RESSEDIMENTAÇÃO NO SUBGRUPO ITARARÉ: TRATOS DE FÁCIES E HIDRODINÂMICA DEPOSICIONAL

Abstract

This paper is a contribution to the resedimentation facies analysis in the Permo-Carboniferous Itarare Subgroup, Parana Basin, southeast Brazil, and it is complemented by a thematic field guide for Porto Feliz region, Sao Paulo State. Two facies tracts were identified. The confined tract (identified by erosional features at the base of the deposits) is composed by a transitional facies set typified by the following end-members: disorganized diamictites, organized diamictites or conglomerates, stratified sandstones, and massive sandstones. To the unconfined tract belong the following transitional spectrum end-members: disorganized diamictites, graded rhythmites, varvic rhythmites and their disturbed equivalents. The origin of resedimentation hydrodynamic process is essentially gravitational. It starts when the glaciogenic deposits are remolded upon flooding by marine transgressions. The unstable remolded deposits are submited to debris flows which evolve to high concentration turbidity currents under confined conditions. At the end of this continuous process the turbidity current interplays with traction, grain interaction and fluidization. The debris flows under unconfined conditions evolve directly to low concentration turbidity currents and from these to diluted suspensions. As the deposition may take place at any moment in those continuous flow spectra, the resultant deposits show continuous transition in their facies characteristics. The presence and abundance of resedimentation facies in the Itarare Subgroup attest that the glaciers were more important functioning as a supply agents than depositional agents.