Geocronological Characterization as a Tool for the Evaluation of Fluvial Capture Occurred in Rio Guaratuba, SP, Brazil

Abstract

This research aims to corroborate with the study of fluvial captures occurring in southeastern Brazil, especially regarding the superficial covering materials that form fluvial morphological features. Samples were collected from the surface coverings of the soils that cover the dry valley or the old Guaratuba river terrace, area of the basin divider between the upper Guaratuba and Rio Claro, for granulometric, morphoscopic, mineralogical and palynological evaluation. Samples of sandy material were submitted to absolute dating through the Optically Stimulated Luminescence (LOE) method, while those of organic material were submitted to absolute 14C dating by Accelerator Mass Spectrometry (AMS). The cover materials were classified in the macromorphological analysis as Gleysols, Podzols, Histosols and Cambisols which contained gravels with more than 1m depth. It occurs the predominance of the sandy fraction in all the horizons described in the granulometric analysis, as well as of quartz and mica in the mineralogical analysis. In the morphoscopic analysis of the sand fraction, the roundness of the quartz grains was observed in all the horizons, indicating that these grains suffered in the past mechanical erosion by current flow. The evaluation of fossilized pollen grains revealed a total of 7 distinct taxon preserved in the dry valley, 1 Gymnosperm and 6 Angiosperms, being the sediments corresponding to the late Pleistocene and Holocene, which indicates the possibility of correlation of the formation of this feature with climatic fluctuations. Systemic studies become important references in elucidating in their results the role of materials that form fluvial morphological features resulting from captures.