Neotectônica e estruturação dos sistemas hidrogeológicos da região de Castanhal/Pa

Abstract

The morphstructural and hydrogeological studies done in two distinct scales, 1:100,000 and 1:25,000, in Castanhal City (PA), the advance on the understanding of the relation between geometric elements of hydrogeological systems and structural elements related to neotectonic events as a base to determine, among other aspects, potential recharge areas of these systems, was allowed. The morphstructural study supported by collected geophysical data showed that the area has a structural control related to a neotectonic pulse responsible for the reactivation of NW-SE-, NE-SW, NS and EW direction failures, which caused anomalies and changes in drainage patterns, and conditioned the establishment of terrain units where river plains, pediplanizadas hills and top-flattened hills jut out. These failures can become compatible in a system of efforts, which generated a geometric formation characterized by tectonic blocks limited by such failures, as well as a kinematic framework of dextral configuration, where in an explicit way extension failures were formed in the NW-SE direction, consolidating important flumes for the recharge of hydrogeological systems. The area is composed of three hydrogeological systems: Superior, characterized as free and found at depths from 2 to 8m; Barreiras varying from free and semiconfined and found from 20m depth, and Pirabas characterized as confined and found at depths from 90 to 120m. These systems present variable depths related to the displacement caused by neotectonics failures. From the confined hydrogeologics systems (Pirabas) to the semi-confined ones (Barreiras) are being largely recharged in the area of Castanhal by natural flumes which are the areas of extension failures and fractures of NW – SE direction. The recharging of the free hydrogeological systems (Superior and Barreiras) occurs by direct precipitation from the rain water in the central-west portion of the study area, in other words, near Couro do Curió river and in the northeast portion near Defunto river.