Aspectos Tectônicos da Deposição de Folhelhos Pretos: Comparação Entre A Formação Irati e o "Chattanooga Shale"

Abstract

A review of lithologic characteristies, enviromments, and tectonic influence on the deposition of black shales is made. A short deseription of the Irati Formation (Lowe Permian of the Paraná Basin, South America), and the Chattanooga Shale (Upper Devonian of the central-eastern part of North America) is presented and the paleotectonic conditions of their deposition are discussed. The paleotectonic conditions of both units are similiar, in spite of the diferences in the paleogeography of the Irati Formation and the Chattanooga Shale. For both units, the black shales that characterize them, were deposited on wide areas of stable platforms, with adjacent stable lowlands that funished the very fine terrigenous material deposited along with organic matter. Positive areas supplies coarse and fine material. The coarse material was trapped in gighly subsident marginal basins and the fine one was drifted onto the platform. Tectonical disturbances of the source area and climatic changes during deposition of the Irati Formation were responsible for the various sedimentary facies which are associated.