A MIDDLE PERMIAN (ROADIAN) LUNGFISH AESTIVATION BURROW FROM THE RIO DO RASTO FORMATION (PARANÁ BASIN, BRAZIL) AND ASSOCIATED U-Pb DATING

The Permian Rio do Rasto Formation (Paraná Basin) crops out in southern Brazil and was deposited under fluvio-lacustrine settings. A singular outcrop located in the Aceguá municipality (Rio Grande do Sul State) represents a sequence of three distinct levels of paleosols in which rhizoliths and a single vertebrate burrow were recovered. The latter has a sub-vertical orientation, a slightly curved shape and a gross morphology and simple architecture that are consistent with aestivation burrows produced by lungfishes. The occurrence of this structure, in association with the features of the paleosols, indicates a seasonal climate with drought events. Additionally, a tonstein layer is interbedded in the paleosol sequence, indicating the influence of volcanic ash falls in the paleoenvironment. Zircons were collected from this level and dated using U-Pb techniques and the obtained age is 270.61 +1.76/-3.27 Ma (Roadian). The paleoenvironmental context of this outcrop is in accordance with a dry, seasonal climate of southwestern Pangaea during the early Guadalupian.