Fraturas, carste e cavernas nos calcários Jandaíra em Felipe Guerra, Rio Grande do Norte

Abstract

Structural and geological conditions were studied to evaluate their influence on the control and evolution of karst features in Cretaceous carbonates of the Jandaíra Formation. The investigated area was the Arapuá limestone outcrop located in the municipality of Felipe Guerra, western part of the Potiguar Basin. The structural arrangement of the fractures shows the existence of four families with preferential strike directions: NW-SE, NE-SW, NS and E-W which coincide with the major fault systems in the Potiguar Basin, as with the direction of caves development in the study area. The Arapuá cave, main cavity of the area, was mapped in detail scale and we carried out the structural survey of existing discontinuities within it. The main galleries that define the cave’s outline, the cracks and stalactites alignments on the ceiling follow the same structural control observed on the outcrop’s surface. A Boolean stochastic simulation applied to the discontinuities in the studied area allowed the generation of three-dimensional graphics to provide a tridimensional (3D) view of the intensity and spatial orientation of structures in three different depths, enhancing the tendency of fracture directions recognized at the surface, with great reduction in the occurrence and quantity of the E-W and N-S oriented fractures with depth. Local structural ar rangement coincides with the regional one observed in the Potiguar Basin, set up by a system of extensional faults that limit structural horst and grabens oriented along NE-SW and NW-SE, inherited from the fragmentation of the supercontinent Gondwana and South Atlantic opening. Small NE-SW faults with dextral directional movement suggest association with reactivated structures in a strike-slip regime. Among the different facies recognized in cross sections of the Arapuá cave, the mudstones and crystalline carbonates correspond to those with greater development of secondary porosity and cavities.