Paleoenvironmental reconstruction of the Lower Mogi Guaçu River Basin (São Paulo State - Brazil), morphopedosedimentary records and fluvial processes

- The interplay between meandering river processes and floodplain shaping processes at landscape scale
- A 130,000 years palaeoenvironmental reconstruction was proposed.
- An interdisciplinary study including soil science, geomorphology and palinology;
- The results pointed to climatic variations during Pleistocene and Holocene periods.

The Mogi Guaçu River rises in Bom Repouso (Minas Gerais State - Brazil) in the Mantiqueira Ridge, and flows into the Rio Pardo river at an elevation of 483 m in Pontal (São Paulo State - Brazil), after running a 530 km long course. Especially along the Lower Mogi Guaçu Basin, the river morphology is extremely sinuous, characterized by intense processes of channel migration, avulsion, abandonment and reactivation of the channel, producing an extensive alluvial plain composed of a series of associated relief forms and sedimentary facies. Among these forms, point bar deposits by lateral accretion, abandoned meanders, paleo-channels and fluvial terraces are notable features. In this sense, the objective of this work was to investigate whether these features could be linked to environmental changes. To reach this goal, soil properties of a catena of the Jataí Ecological Station (Luiz Antonio - São Paulo State) were analyzed in four sectors: Slope, Terrace I, Terrace II and Alluvial Plain. The results from grain-size determination, geochemical and isotopic studies, dating, paleopalynology, coal fragments and micromorphology are presented in this paper. From these analyses, a paleo-environmental evolution divided in three stages is proposed for the area: 130,000 YBP (Upper Pleistocene), when the Mogi Guaçu River base level was approximately 6 m above the present one; a drier second phase 10,250 years BP (Lower Holocene), when an organic horizon was formed inside of an abandoned meander (oxbow lake), and a third phase, 2096 YBP (Upper Holocene), of reactivation of a warm and humid climate that promoted the development of a two meters thick Typic Udifluvent in a sector where the Mogi Guaçu River no more floods due to the incision of its thalweg, reaching more than six-meters depth in the last 130,000 years BP. Thus, this paper used a fluvial geomorphologic approach and its interplay with climate to understand how the landscape was shaped from Upper Pleistocene to Holocene, however, Neotectonics might have played a relevant role as well, not only in the Mogi Guaçu River Basin, but also in the Paraná Sedimentary Basin.