Estudo paleoambiental dos depósitos cenozóicos e caracterização dos minerais de argila da região de Itambí, Itaboraí-RJ

Abstract

The purpose of this study is to characterize of the clay minerals found in the Itambi-Itaboraí region and concomitantly, offer a depositional pattern for the Macacu Formation deposits. In order to reach this goal it was carried out a facies characterization at the studied outcrops (the outcrops which were studied) by means of through the description of sedimentological profiles and the interpretation of the main facies identified in the field. A granulometric analysis of the sandy fraction was carried out for the laboratory study. Following this course of action, a pipetting technique was carried out on the fraction with the objective of concentrating the clay minerals only. In addition to the previous procedures the samples were exposed to a diffractometer and to an electronic microscope scanning. .These analyses were carried out with the purpose of adding information as much for understanding the depositional reality of the Itambi area, in the Macacu Formation, as much for identifying the minerals in the existing clay minerals. The results of this study showed that among the outcrops examined, the ITA 7 profile presents a series of the necessary conditions to distinguish four depositional systems which are accountable for the deposition in the Itambí area, as follows: A) Lacustrine: constituted basically by facies Lam and Lal. B) Alluvial Fan: formed by facies, Aci, Lam, Lal, Acm, Aca; C) Fluvial Duct comprises the facies Aca, Asm and; D) Gravel Braided Fluvial System (more recent torrential flow regime) includes the Acm e Aca facies. Under the mineralogical point of view, the mineral which was predominant in the examined facies was the kaolinite group. Only four facies (Afm, Afcat, Lam 2 and Aca), out of a total of thirteen, did not present a predominantly kaolinitic nature in their results. Based on these observations, it is possible that the lacustrine deposits of montmorillonitic nature, showing greenish color and laminated structures which were identified at the Itambí base strata may favor the ceramic industry since they confer it high plasticity. Equally, the facies which showed a predominance of kaolinite are recognized for presenting a favorably smaller granulometry, with the formation of an early vitreous phase which can unite the mineral particles and, consequently, is less susceptible to cracks during the drying process of the ceramic materials.