CLAY MINERALOGY OF THE SEDIMENTARY ROCKS OF THE PARANÁ BASIN, BRAZIL

Abstract

The clay mineral composition of 1,052 core samples from 43 wells drillcd in the eastern and southern parts of the Paleozoic Parana Basin have been investigated by X-ray diffractometry. The clay mineral suites are characterized by a mixture of illite, chlorite, mixed-layer illite-montmorillonite, which are the dominant minerals, with subordinate amounts of kaolinite, montmorillonite and mixed-layer chlorite-montmorillonite. Most of the clay minerals are detrital but, at least, some of the illite, kaolinite, and corrensite have been diagenetically formed. Illite and chlorite are found throughout the section. Mixed-layer illite-montmorillonite are well developed in the Permian Rio Bonito and Palermo Formations, becoming rarer in older formations due to diagenesis or climatic conditions. Kaolinite occurs in the continental Devonian Furnas Formation and in the deltaic, and near shore facies of the Rio Bonito Formation. Smectites are important in some formations of the Rio Grande do Sul and Sao Paulo States and in the upper part of stratigraphic column, as a result of different regional sedimentary or volcanic source areas and/or climatic conditions. Corrensite generally occurs associated with the oolitic limestones of the Permian Teresina Formation, suggesting diagenetic processes in marine environment. Such minerals as expansive chlorite and irregular mixed-layer chlorite-montmorillonite suggest different stages of alteration of chlorite and magnesian chlorite suggests diagenesis. Hydrocarbon shows in th e Parana Basin have been reported especially in the Rio Bonito Formation, and are thought to be related to the greater abundance of expansive clay minerals.