Controle estrutural e faciológico na espeleogênese em calcários da formação Jandaíra (Bacia Potiguar): Lajedo do Rosário, município de Felipe Guerra–RN

Abstract

This work represents a geological and speleological study in the municipal district of Felipe Guerra in Rio Grande do Norte, which has shaped up a typical karst on limestone of the Jandaíra of the Potiguar basin. The research aimed to identify factors that contributed to the genesis of the complex of caves in the area. At first it was performed a structural analysis based on satellite imagery (digital globe), digital terrain model (SRTM) and existing maps. It was identified that a series of regional structures played a big role in geomorphological modeling of the region, highlighting the retreat from the south rim of the basin, waterfalls, Apodi-Mossoró River canyon and evidenciation of calcareous tufa, and the development of karst features. The regional statistical analysis show there is greater representation for the families of lineaments oriented to NW-SE (59%) and NE-SW (33%), these structures are associated with Afonso Bezerra and Carnaubais systems of faults. In the detail analysis on the Rosario outcrop almost 3,000 structures were identified, predominantly oriented to NW-SE (50%) NE-SW (24%) and NS (20%). The ranges of greater significance, with reference to the sinistral transtrasion fault NE-SW that cuts the outcrop, indicates that these structures were propagated as sinistral shear Riedel fractures. The histogram comparison between regional structures and the Rosary outcrop shows that their higher frequencies are not coincident, indicating that most of the discontinuities present in the outcrop have been caused by the influence of local tectonic deformations. The analysis of all of the Rosary outcrop gifts caves shows that their developments are not limited to preferred standards of guidance structures, the most important comes from the intersection of structures, mainly with the orientation NW-SE, NE-SW and E-W. In the second phase of the research, the characterization of carbonate strata of the Rosary outcrop, based on indexes of physical tests, uniaxial compression, wear abrasion, chemical attack, petrography, chemical analysis and diffraction of x-rays showed that the cave Desafio layer was shown to be highly resistant in relation to the other levels studied. The high resistance in the Cave level is attributed to chemical sedimentation (carbonate mud) that originated the layer and the mineral dolomite in abundance. The occurrence of caves in such a tough statement is explained by the existence of centimetrics voids concentrations originated by dolomitization process occurred by diagenesis. These voids during the dissolution of evolution in karst, tend to grow and to unite, forming caves.