Drainage anomalies mapping: evidences of lithological and structural control in Cotia's river drainage basin in Cotia-SP, south-eastern Brazil

Abstract

This paper examines the geomorphological setting of the Cotia’s drainage basin, in Cotia (São Paulo state). The purpose of this investigation is study the evolution of the drainage network of Cotia’s high course, located at Reserva Florestal do Morro Grande (RFMG), where anomalies of the drainage are found, with a sequence of inflexions of 90 degrees in the channel. The study area is regionally inserted at Ibiúna’s plateau, a geomorphological compartment represented by elongated hills of medium and high declivities, with heights between 860 to 1075 meters. This unit is composed by neoproterozoic granites and migmatites, that can indicate the influence of joint systems on the drainage pattern. Beside the lithological influence like a potential control of this net, there is the structural factor, expressed by the existence of faults, integrated to the Caucaia Fault Zone, which cross the river in direction NE-SW. As investigation methods, air-photo interpretation and digital mapping was adopted (in scales 1:25000 and 1:50000, respectively), with the intention of identifying geomorphological features that contribute with the understanding of the involved process in the present configuration of this drainage net.