Evolution of an estuarine valley to barrier-lagoon system promoted by tidal prism change during a transgressive event (Lower Permian, Paraná Basin)

Abstract

In modern marine marginal environments, the coastal morphology directly influences the tidal and wave processes. In this paper we present an example of an ancient coastal zone where the change in coastal morphology controlled the tidal range. This study focuses on the Permian Rio Bonito Formation in the southern Paran´ a Basin, where the major coal deposits of South America are located. Sedimentological and stratigraphical approaches were applied to cores drilled in the Candiota paleovalley area. We describe the stratigraphic architecture of a transgressive event of the Lower Permian (Rio Bonito Formation). Two third order depositional sequences were identified, which show differences in the paleoenvironmental record. In the lower sequence, associated with the infilling of an incised valley, facies related to fluvial and tidal currents are dominant. In a micro-tidal inner sea context, tidal range is amplified in a funnel-shaped valley. In the upper sequence, already evolving in linear coastal conditions, evidence of tidal depositional processes almost disappear, and the sedimentation becomes dominated by wave processes, thus a coastal barrier system associated with lagoons and swamps is established. Our study, besides detailing the paleoenvironmental evolution of the sedimentary infilling of an incised valley, also provides for a better understanding of the origin of southern Brazil coal.