Provenance analysis of the Guaritas Group (RS) conglomeratic sandstones: implications for the paleoclimate and paleogeography of the Eocambrian Central Camaquã sub-basin

Abstract

The Camaquã Supergroup, located in the central-south region of Rio Grande do Sul, Brazil, constitutes a rift-type post-orogenic sedimentary basin, whose deposition occurred in a continental environment between the Ediacaran and the Eocambrian. The upper succession of the Camaquã Supergroup is represented by the Guaritas Group, a unit formed by fluvial, eolian and alluvial fan deposits that keeps important records of the sedimentation right after the end of the neoproterozoic orogenesis that gave rise to the Gondwana supercontinent. The objective of the present work was to apply sedimentary provenance analysis in conglomeratic arenites and conglomerates of the Guaritas Group, in order to explore the climatic and tectonic evolution history of this unit. Based on the pebble compositional data, two main source areas were recognized for the deposits of this unit, a more distal one located to the north, related with a trunk river system parallel to the basin main axis, and a more proximal one located to the east, related to transversal fluvial systems and alluvial fans at the border of the basin. The comparison of the provenance data with previous studies on facies and paleocurrents suggests that, during the entire evolution of the east border of the basin, there was a same transversal fluvial system, whose catchment area suffered significative reductions due to the reactivation of the east border fault during the deposition of the Varzinha and Pedra Pintada Formations. The Serra do Apertado Formation, the upper unit of Guaritas Group, shows a high correlation between the variation of quartzose and non quartzose pebbles composition, and it was attributed to a variation between more humid and more arid climatic conditions.