Drainage evolution in the Piraí depression (southern Brazil): evidence for headward erosion in large south american river systems

Abstract

The long-term evolution of rivers draining westward from Brazilian Great escarpment remain unclear and one of the main questions is how western draining rivers organized and defined their modern courses. In this study, we evaluated how the Piraí Depression (PD) evolved and how rivers draining the PD interior defined their valleys and became an important contributing area for the Paraná River catchment. We used three sets of data: (1) topographical metrics (ks(n), knickpoints, local relief, χ-index values, Gilbert metrics, Swath Profiles and Seppômen Maps); (2) relief and river morphology (elbows and low-divides) from remote sensing derived data; and (3) sedimentologic analysis from a drainage capture previously identified with vibro-corer drilling. Ks(n), local relief and χ indices, and morphological evidence, point to an ongoing process of drainage rearrangement all over PD as it has been continuously eroded by Tibagi, Cinzas, Itararé and, mainly the Atlantic draining rivers from the Ribeira do Iguape River System. Morphometric, morphological and sedimentologic data imply long-lasting recurrence of captures and divide migration. The oldest capture evidence in the study area corresponds to the incision of the Iapó River which created the Guartelá Canyon. At least three generations of captures followed, and the younger generation is exemplified by the Maracanã-Jotuba capture as shown by the fieldwork data and described sedimentary facies. The field-documented underground capture illustrates the progressive abandonment and valley filling of the Maracanã River and capture by Jotuba river. Headward erosion and groundwater sapping are crucial for drainage (re)arrangements. In the PD drainage transition from endorheic to exorheic system was a direct result of captures. Atlantic rivers have greater erosion power and also migrate westward capturing areas from Paraná-La Plata which does not prevent drainage rearrangements to take place between westward-draining rivers.