Luminescence Chronology of Terrace Development in the Upper Parana River, Southeast Brazil

Abstract

The Parana River has been extensively studied in terms of hydrological and sedimentological characterization. However, the geological history of its fluvial plain is poorly understood due the lack of geochronological data. Most of the studies are focused in the low and middle reaches, whereas the region upstream of the Porto Primavera dam is an almost unknown area in terms of geomorphic evolution. Thus, the main aim of this study was to investigate the succession of geological events responsible for the evolution and current configuration of the fluvial system of the Upper Parana River, between the Jupia and Porto Primavera Hydroelectric Power Plants (Sao Paulo and Mato Grosso do Sul states). In order to achieve this goal, we used an integrated approach including remote sensing data, geomorphology, sedimentology, geochronology and bathymetric profiles. Four geomorphological compartments were identified and three of these compartments were dated by Optically Stimulated Luminescence (OSL): Unit 1, raised terrace with circular and semicircular ponds (similar to 150 ka); Unit 2, intermediate terrace with small ponds and waterlogged areas (similar to 60 ka); Unit 3, low terrace with preserved paleochannels (similar to 39-35 ka); and Unit 4, current river plain (> 9 ka). The geomorphological units were correlated with previous studies downstream of the studied area and their sedimentary characteristics and depositional ages suggest that their genesis is linked to changes in climatic and hydrological conditions during the Late Quatemary. Units 1, 3 and 4 are considered extensions of the geomorphological units Taquarucu, Fazenda Boa Vista and Rio Parana, respectively. Unit 2 is a compartment with unique morphological characteristics, therefore not correlated with units presented in previous works. Further, two main knickpoints were identified, suggesting an important control in the sedimentation and development of the terrace levels. Therefore, this work brings new data about the fluvial plain of the upper reach of the Parana River, that allows to interpret that the development of terrace levels and floodplain are strongly controlled by climate changes occurred during the Late Quaternary.