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 (30.3O 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 (ag5 = 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 (ass = 13").The red beds involved in this study are correlated with red beds from the Corumbatai Formation (State of Parand, 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, (ag5 = 4") which followed the South American Late Palaeozoic polar shift.
In this paper we present palaeomagnetic data from 87 hand samples collected in a sequence of tuffs and shales (Suri Formation) of Llanvirnian age, exposed in north-western Argentina (27" 47'S, 68" 06'W). After cleaning, the majority of samples showed reversed polarity and yielded a palaeomagnetic pole at 5.9" E, 8.5" S (ag5 = 5.9'). They also showed reversals of declination and inclination at the top of the sequence, which we have associated with geomagnetic excursions. Whole rock K-Ar age determinations suggest an age older than 416 2 25 Myr for the Suri rocks. The predominant reversed stable remanence of these rocks is consistent with the reversed polarity reported for Early Llanvirnian rocks from USSR. The palaeomagnetic pole for the Suri Formation is consistent with the interpretation that Gondwana was a single unit in Early Palaeozoic times.Palaeomagnetic data from 27 hand samples collected from 10 igneous units of Late Silurian-Early Devonian age (fluzorco Formation), exposed in the same area, are also given. The majority of the igneous units showed reversed polarity after cleaning. The positions of VGP's for the fiuEorco igneous units are scattered and they are not used for geodynamic interpretations. Whole rock K-Ar age determinations suggest ages of 416 k 25 and 360 k 10 Myr for two igneous units of the fiuGorco Formation.
Summary. Stable components of magnetization have been isolated in 15 lava flows (mean K‐Ar age 123 ± 4 Myr) from the alkaline sequence outcropping at El Salto‐Almafuerte, Province of Cordoba, Argentina. Magnetic and geologic stratigraphy, as well as K‐Ar ages indicate that this sequence was probably extruded in the Lower Cretaceous during the first volcanic cycle of the Sierra de los Cóndores Group (Vulcanitas Cerro Colorado Formation). The palaeomagnetic pole‐position for El Salto‐Almafuerte lava flows, computed from the mean of 15 virtual geomagnetic poles and denoted SAK7, is: 25° E, 72° S (k= 35, α95= 6.5°); it is fairly close to other Lower Cretaceous palaeomagnetic poles for South America. The elongated distribution of Cretaceous palaeomagnetic poles suggest recurrent drift for South America in early Cretaceous time. The palaeomagnetic and radiometric data for the igneous rocks from El Salto‐Almafuerte support the magnetic reversal time‐scale for the early Cretaceous suggested by oceanic magnetic lineations.
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