Conglomeratic deposits of the Paleo Tietê River: event of fluvial aggradation during the evolution of the São Paulo peripheral depression
DOI:
https://doi.org/10.11606/issn.2316-9095.v19-155306Keywords:
Conglomeratic deposits, Sedimentary provenance, Optically stimulated luminescence, Facies analysis, Tiete River, CenozoicAbstract
The conglomerate deposits located near the district of Laras, São Paulo, cover wide flat-topped hills with altitudes between 500 and 570 m. They occur in discordance on older Piramboia and Teresina formations of the Parana Basin and are consisted of poorly selected sandy matrix polymeric orthoconglomerates. The provenance analysis performed showed the predominance of well-rounded and oblate silex clasts, quartzite and quartz vein clasts, suggesting long-distance transport. Statistical analysis revealed a higher frequency of transport-resistant lithotypes in the southeastern portion of the area. In the northwest portion, less resistant clasts predominate, represented by oolite and coquina, suggesting erosion of the Teresina Formation and short transport from Paleozoic terrains existing in the São Paulo Peripherical Depression. Optically stimulated luminescence (OSL) data allowed for a minimum age of 371.4 ± 27.5 ka for the unit. Conglomerate deposits are interpreted as the product of deposition in large tributary fluvial channels, or even of a main trunk channel, of an extensive fluvial depositional system with depositional paleomoving diving to the southwest of São Paulo State. This predecessor river system of the current Tietê River, coming from the northeast, had drainage area in precambrian lands located to the east of the occurrence area of the Paleozoic units. Due to their location and size, these deposits represent an important phase of fluvial alluviation in the geological history of the Tietê River, a sedimentation event that occurred during the long-term denudation process that gave rise to the São Paulo Peripherical Depression during the Cenozoic.
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