MiddleLate Permian magnetostratigraphy from the Parana Basin, South America

Following the waning of Late Paleozoic Ice Age in southwest Gondwana at ca. 297 Ma, the intracratonic Parana Basin has been filled by ca 1.5 km, deltaic to shallow-water deposits spanning the whole Permian and the end of Kiaman Superchron. Geomagnetic Polarity Time Scale of this interval is still being refined and the Paraná Basin may provide some useful independent contributions to the proposed time scales. Benefitting a regional coring program by the Brazilian Geological Survey, paleomagnetic analyses have been performed a on a 300-m-long core which retrieved Middle to Late Permian deposits of the Passa Dois Group. Sample demagnetization of 147 samples revealed a stable, dual polarity characteristic component (ChRM), isolated at temperatures higher than 450 °C and interpreted as primary detrital remanence. Core azimuth orientation and determination of ChRM declination was allowed by a low-temperature component which is consistent with Brunhes Chron inclinations at drilling site. A total of 8 reverse polarity intervals were identied, the lowermost of which (up to 110 m thick) correlates to the Kiaman Superchron. The overlying Illawarra succession is dominated by a reverse polarity magnetization with thin (45 m thick) normal polarity intervals. Available U-Pb dating on volcanic zircons from literature provided independent chronologic constraints and allowed to constraint the onset of Illawarra reversals to ca. 270 Ma, in fair agreement with the age of 269 Ma obtained in the Karoo Basin. Estimated duration of Illawarra normal polarity magnetochrons as recorded in the Parana Basins is in the order of 0.5 million years.