PALAIOS, 2018, v. 33, 69–84 Research Article DOI: http://dx.doi.org/10.2110/palo.2017.050 A MIDDLE PERMIAN (ROADIAN) LUNGFISH AESTIVATION BURROW FROM THE RIO DO RASTO FORMATION (PARAN ´ A BASIN, BRAZIL) AND ASSOCIATED U-Pb DATING HEITOR FRANCISCHINI, 1 PAULA DENTZIEN-DIAS, 2 MARGOT GUERRA-SOMMER, 1 RUALDO MENEGAT, 1 JO ˜ AO ORESTES SCHNEIDER SANTOS, 3 JOSELINE MANFROI, 4 AND CESAR LEANDRO SCHULTZ 1 1 Instituto de Geociˆ encias, Universidade Federal do Rio Grande do Sul, Avenida Bento Gon¸ calves, 9500, Porto Alegre, Caixa Postal 15.001, CEP 91501-970, Brazil 2 Instituto de Oceanografia, Universidade Federal do Rio Grande, Avenida Ita ´lia Km 8, Rio Grande, CEP 96201-900, Brazil 3 Centre for Global Targeting, University of Western Australia, 35 Stirling Highway, Perth, 6009, Australia 4 Programa de P´ os-Gradua¸ ca ˜o em Ambiente e Desenvolvimento, Centro Universita ´rio UNIVATES, Lajeado, CEP 95900-000, Brazil email: heitorfrancischini@hotmail.com ABSTRACT: The Permian Rio do Rasto Formation (Parana ´ Basin) crops out in southern Brazil and was deposited under fluvio-lacustrine settings. A singular outcrop located in the Acegua ´ 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 þ 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. INTRODUCTION The Brazilian Rio do Rasto Formation (Parana ´ Basin) has several records of terrestrial fauna and flora, indicating a continental paleoenviron- ment in southwestern Pangea during the middle to late Permian (e.g., Barberena et al. 1985; Holz et al. 2010; see online Supplemental file). One of the main fossil-bearing areas of this unit is the region of the Bag´ e and Acegua ´ municipalities (Rio Grande do Sul State; Fig. 1), in southernmost Brazil. In spite of the presence of plant and vertebrate macrofossils in the Bag´ e-Acegua ´ region (e.g., Ara´ ujo 1985; Dias and Barberena 2001; Cisneros and Dentzien-Dias 2008), the biostratigraphic relationships between the Rio do Rasto Formation and other Guadalupian–Lopingian units worldwide and even between the fossiliferous outcrops within this formation are still conflicting (e.g., Cisneros et al. 2005). Part of this problem is due to the lack of geochronological data in association with fossils and the huge geographical area of exposure of the entire formation (Lucas 2017; Martinelli et al. 2017). Historically, the vertebrate fossils of the Bag´ e-Acegua ´ region were considered part of the Acegua ´ Local Fauna (sensu Barberena et al. 1985) which was used in an attempt to correlate the tetrapod-bearing strata of southern Brazil with the deposits of Russia and South Africa (Barberena et al. 1985; Langer 2000; Cisneros et al. 2005; Langer et al. 2009; Dias-da-Silva 2012; Boos et al. 2013, 2015; Martinelli et al. 2017). However, collection data of several specimens are missing and, consequently, the Local Faunas could group non-contemporaneous taxa. Consequently the division of the Rio do Rasto Formation in these assemblages was discouraged (Boos et al. 2015; Martinelli et al. 2017). In spite of the presence of tonstein beds in the Bag´ e-Acegua ´ region, there were few studies that provided absolute ages for the deposition of the Rio do Rasto Formation. Rocha-Campos et al. (2006) proposed an age of 275.1 6 5.4 Ma, but they do not provide the exact area of study, disabling further considerations about the fossil record of this unit. Other studies performed dating for detrital zircons, providing only maximum deposi- tional ages of 269 6 2 Ma (Alessandretti et al. 2016) and 255 6 2 Ma (Canile et al. 2016). Additionally, the lack of high-precision mapping in the Bag´ e-Acegua ´ region is critical for the recognition of Rio do Rasto Formation deposits. For example, in the lithostratigraphic framework proposed by Gordon (1947) and Schneider et al. (1975), the Rio do Rasto Formation occurs in the Parana ´, Santa Catarina, and Rio Grande do Sul states (Fig. 1) of southern Brazil. However, whereas in Parana ´ and Santa Catarina the unit can be divided into two members (the lower Serrinha Member and the upper Morro Pelado Member), in Rio Grande do Sul it is considered undivided (e.g., see the stratigraphic chart of Schneider et al. 1975, p. 43). The outcrop described here does not shed light on this discussion, since no macrofossil taxon is shared with other outcrops and its facies apparently do not continue laterally in that region. Nevertheless, the radiometric age presented here can be used as a datum for the area, improving correlation with other outcrops within the Parana ´ Basin, as well as coeval stratigraphic units in other basins. In this paper, we aim to analyze this newly discovered outcrop at the margin of BR-153 highway, which includes a burrow and distinct pedogenetic morphologies, such as rhizoliths. This burrow represents the first record of a lungfish aestivation burrow in the Permian of Brazil, and its association with rhizoliths is an important remark on the study of the paleoenvironments of the Rio do Rasto Formation. Additionally, zircon crystals from a tonstein layer that is interbedded with paleosols at the site are radiometrically dated by SIMS using the U-Pb system. Furthermore, we also discuss the paleoenvironment and paleo- climatic scenario in which the Bag´ e-Acegua ´ beds were deposited using a multidisciplinary (ichnological, geochronological, and sedimentological) approach. Published Online: February 2018 Copyright Ó 2018, SEPM (Society for Sedimentary Geology) 0883-1351/18/033-069/$03.00