No abstract

Pyroclastic levels are descripted in Sierras Australes outcrops and Claromeco Basin sub-surface records, interbedded with mudrocks and coal beds in the base of the Tunas Formation sequence that correspond to the Permian South West margin of Gondwana. The pyroclastic levels classify as fine tuff. SHRIMP zircon ages obtained are 291.7 ± 2.9 Ma in the outcrop and 295.5 ± 8.0 Ma in the subsurface. These ages are consistent with other zircon SHRIMP ages of other outcrops tuff of the Tunas Formation, with Permian flora, and with tuff ages of correlated Gondwana areas, in the Paraná, Karoo and Paganzo basins. These data, in addition with other geological evidences, support a tectonically active and changing