Study of the rates of sedimentation of Teresina and Rio do Rasto formations - Paraná Basin

Abstract

This paper presents a stratigraphic analysis on the Permo-Triassic uppermost section of Paraná Basin (Teresina and Rio do Rasto formations). These twoo units present anomalously high sedimentation rates if we consider the biochronostratigraphic data currently used as input to basin modeling programs. The rate of sedimentation of Teresina and Rio do Rasto formations (150 to 500 m/M.y) is far above the average presented by the lower sedimentary units (about 60 m/M.y). High sedimentation rates, higher than 100 m/M.y, are commonly related to deposition in rift-type basins; thus, dissimilar to Paraná Basin, supposedly an interior sag basin at the time of the Permo-Triassic. The Corumbataí Formation, stratigraphically correlated to Teresina and Rio do Rasto formations in the northem part of the basin, was recently dated as Camian (Late Triassic), based on fish remains. By using this new datum as input, the sedimentation rates of the Teresina and the Rio do Rasto formations drop to a leveI close to the average of the remnant stratigraphic units of the basin: around 50 m/m.y. This paper is concemed with presenting new stratigraphic and sedimentologic evidences, suggesting that Teresina and Rio do Rasto formations are younger than what has been currently accepted. The stratigraphic analyses were perfomed by applying backstripping and geohistoric techniques from BaSS (Basin Simulation System), a basin modeling program developed DEPEX/CENPES/PETROBRAS.