Palaeomagnetism of a sequence of red beds of the Middle and Upper Sections of Pagnazo Group (Argentina) and the correlation of Upper Palaeozoic‐Lower Mesozoic rocks

Abstract

Palaeomagnetic data from 182 hand samples collected in a rock sequence of about 620‐m of red beds of Late Palaeozoic to Early Triassic age exposed in north‐western Argentina (30.3° S 67.7° W), are given. After cleaning, the majority of the Upper Palaeozoic samples (Middle Section of Paganzo Group) show reversed polarity and yield a palaeomagnetic pole at 78° S 249° E (α95= 3°). They also record a polarity transition which we have correlated with the Middle Permian Quebrada del Pimiento Normal Event. The position of the palaeomagnetic pole and the K‐Ar age of a basalatic sill at the base of the sequence support this correlation. Stable remanent magnetization has been isolated in the majority of samples from the Upper Section of the Paganzo Group; it is predominantly reversed and reveals three normal events and also three geomagnetic excursions suggesting an Illawarra Zone age (post Kiaman, Late Tatarian‐Early Scythian). The palaeomagnetic pole of the reversely magnetized samples is located at 75° S 285° E(α95= 13°). The red beds involved in this study are correlated with red beds from the Corumbataí Formation (State of Paraná, Brazil) and with igneous rocks from the Quebrada del Pimiento Formation (Province of Mendoza, Argentina). The South American Middle and Upper Permian, Upper Permian—Lower Triassic, Lower, Middle and Upper Triassic and Middle Jurassic palaeomagnetic poles reflect a quasistatic period with mean pole at 82° S 244° E, (α95= 4°) which followed the South American Late Palaeozoic polar shift. Copyright © 1977, Wiley Blackwell. All rights reserved