Sedimentary fluvial processes at the margin of an eolian sand sea: the example of the Botucatu Formation, Paraná Basin

Abstract

The Upper Jurassic to Lower Cretaceous Botucatu Formation of the Paraná Basin consists primarily of trough cross-bedded eolian sandstone deposited in an intracontinental desert. In southeastern Brazil, an unusual occurrence of conglomerate and coarse-grained sandstone unconformably overlies the Neoproterozoic basement and is overlapped by volcanic rocks of the Serra Geral Formation. This represents one of the few documented occurrences of fluvial facies described for the Botucatu Formation in the northern part of the basin. To determine its depositional system and source area, we conducted facies and paleocurrent analysis, detrital grain modal counting, macroscopic provenance, and conventional heavy mineral analysis. The integrated analysis suggests that the studied succession was deposited by an ephemeral fluvial system at the margins of the extensive dune fields of the Botucatu paleodesert. Paleocurrent data and detrital composition indicate sediment dispersal toward the SE, with a possible source area associated with a recycled orogen to the NW (Brasília Belt). Although ephemeral rivers acted as important sediment suppliers for this continental-scale desert, recycling of eolian sediments by fluvial systems is not ruled out. Finally, using a multi-proxy approach, we present a paleogeographic scenario for the northern margin of the Botucatu paleodesert during the last period of Gondwana, prior to its initial rifting.