Olavarría County

Abstract

In the Sierras Bayas Sector clay deposits correspond to the Olavarría Formation and to the Cerro Negro Formation, both of Neoproterozoic age. They represent important sedimentary deposits of the Tandilia System because of their extension and technological applications. The Cerro Largo Formation is spread along the Sierras Bayas area and it consists of three units separated by transitional contacts. Geologic-stratigraphical detail studies led to the redefinition of the unit 3 of the Cerro Largo Formation considering it as a separate unit and named Olavarría Formation, studied in various localities of the Sierras Bayas. The unit is limited by erosive unconformities that separate it from the underlying unit (Cuarcitas Superiores) and the overlying one (Loma Negra Formation). MISS, confirm the presence of algal mats also in the Olavarría Formation. X-ray diffraction, optical, microscopy and SEM have been performed on the clay deposits. At La Pampita quarry, the finding and study of a mud bed—connected to several mud pipes—intercalated in the Loma Negra Formation limestones—are attributed to upward mud injection from the underlying Olavarrıía Formation (telogenesis). In general, the clays have low plasticity index. They have low-refractoriness, and are classified as varied red clays and varied ocher clays. They are used in red ceramics. The Cerro Negro Formation has been found in the subsoil and by the opening of several quarries near the Cerro Negro village. The Cerro Negro Formation was divided in two depositional systems separated by an irregular paleosuperface: the Lower Depositional System and the Upper Depositional System. The mineralogical composition of the clays is different in the two depositional systems. Technological tests have been carried out in “composite” samples (stocks) for each of the depositional systems. The clays of the two depositional systems present similar Pyrometric Cone Equivalent (PCE). They are exploited in the area of Cerro Negro, with excellent results and large reserves, for their use in the manufacture of ceramic floor coverings.