Neotectonics and channel evolution of the Lower Ivinhema River: A right-bank tributary of the upper Paranل River, Brazil

The Ivinhema River, an important right-bank tributary of the upper Paraná River, cuts a series of terraces, geomorphic surfaces, floodplains and associate features. Through terrace mapping, sediment composition, absolute (14C, TL) dating and morphostructural analysis, this paper presents the composed longitudinal profile and the structural analysis of the lower course of the Ivinhema River. The tectonic model of the study area constitutes a sequence of NW tilting fault-blocks formed from antithetic faults that control channel sinuosity, longitudinal profile, floodplain distribution and valley asymmetry. The area began to be structured during the Paleocene with formation of the oligomict conglomerate, probably under an arid climate. Another tectonic reactivation in the Mio-Pliocene boundary defined the divides of the Upper Paraná and Paraguay River basins, with formation of the polymict conglomerate. An active depositional phase taken place at the Tertiary–Quaternary limit produced the massive reddish clayey sand sediments very common in the area. During the Late Pelistocene (42.5 ± 1.7 and 31.1 ± 1.7 ka BP), the Paraná and Ivinhema rivers constructed a sedimentary sequence of gravelly sand deposits in a braided channel environment. At the beginning of the Holocene a new tectonic pulse, lifted up a group of blocks parallel to the Paraná River valley, developed a series of antithetic faults. Tectonic intensity associated with the pluvial stage (Hypsithermal phase between 8 and 6 ka) changed the channel pattern of the river from braided to meandering. Channel evolution during the Late Pleistocene and Holocene was also influenced by climatic changes.