Formação corumbataí na região de rio claro/sp: Petrografia e implicações genéticas

Abstract

The Corumbataí Formation that outcrops in Rio Claro (São Paulo State, Brazil) is represented predominantly by clayey siltstones interbedded with sandy siltstones, consisting of illite, quartz, feldspars, carbonates, hematite, montmorillonite, chlorite and zeolites, of authigenic and/or detrital origin. Textural and especially mineralogical variations along the Corumbataí Formation in this region allow to divide it in five mineralogical-textural levels proposed in this paper. The textural and morphological relations between detrital and authigenic components suggest transport in arid environment, with source in area of gentle topography without strong fluvial influence, creating sediments that were accumulated in a shallow, extensive epicontinental sea with evidences of subaerial exposure already in the basal layers, and possible connection to the ocean. It also suggests that the water depth decreased progressively towards the top of sequence, with variations due to the influence of tides and/or storms. The mineralogical composition combined with textural aspects suggest that the Corumbataí Formation was subjected to thermal effect after lithification, promoting mineralogical transformations, hydrothermal alteration and formation of hydraulic breccias caused by the basic magmatism that originated the Serra Geral Formation.