River Capture, Palinology, Geochronology, Paleoenvironmental indicators

The research aimed to evaluate the paleoindicators of the capture process of the Guaratuba River, located in a humid tropical environment. Morphometric aspects and sedimentary and organic materials covering the surface of the dry valley were used as explanatory paleoenvironmental indicators. Samples were collected in the basin divide between the upper Guaratuba and the Claro River, for integrated evaluation of macromorphological, granulometric, morphoscopic, mineralogical, geochronological and palynological data. The samples of sandy material were subjected to absolute dating by Optically Stimulated Luminescence (OSL), while those of organic material were subjected to absolute dating of 14C. The covering materials were classified in the macromorphological analysis as Gleysols, Spodosols and Cambisols. The Spodosol presents itself as a paleosol and the Ortstein horizon as a lithostratigraphic indicator. In the granulometric analysis, the sand fraction predominated in all horizons described, as well as quartz and mica in the mineralogical analysis. In the morphoscopic analysis of the sand fraction, extensive rounding of the gravels and quartz grains was observed in all horizons, which indicates that these sediments suffered mechanical erosion in the past by current flow or torrent deposition, indicating paleoclimate and water conditions different from those of today. The morphometric characteristics of the basins attest to the rejuvenation of the Guaratuba basin in response to capture. The dates indicate specific humid periods of the Holocene, Pleistocene and Last Glacial Maximum linked mostly to the precipitation conditions in the Southeast region. The covering materials of the dry valley, as well as the hydrodynamics of the river channels, have been worked by the humidity cycles in the system for at least 36,500 years B.P. It is possible to link the change in the base level between the rivers and the consequent capture of the Guaratuba to the Last Glacial Maximum, approximately 25,000 years B.P. The taxon assembly formed by Podocarpus sp, Ilex sp, Symplocus sp, Weinmannia sp, Myrsine sp, Alchornea sp, Mytenyus sp, Hedyosmum sp, Myrtaceae, Poaceae and Asteraceae families respond as indicators of humid and/or flooded paleoforests and cold and humid paleoclimates. The taxa found, for the most part, adapted to cold and humid forest environments and constantly or seasonally flooded, indicate an ancient marshy region in the current dry valley. Captures are essential for the evolution of the Serra do Mar and the coastal plain in Southeast Brazil, having as a driving force the humid regional climate condition. The use of the systemic approach for the study of captures, based on interdisciplinary techniques, becomes essential to elucidate in its results the positive response of paleoenvironmental indicators at regional and local levels.