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Disponível on-line no endereço www.igc.usp.br/geologiausp -29 -Resumo O topo da Formação Rio do Rasto, Bacia do Paraná, corresponde ao Membro Morro Pelado, unidade composta pela associação de depósitos fluviais, eólicos e lacustres. A fim de retratar os elementos deposicionais presentes e caracterizar o estilo de sedimentação fluvial, uma análise faciológica foi realizada na faixa de afloramentos do leste dos estados de Santa Catarina e do Paraná. O Membro Morro Pelado é formado por quatro associações litofaciológicas: A, B, C e D. A associação litofaciológica A corresponde aos depósitos de canais meandrantes, presente na zona intermediária de um sistema fluvial distributário. A associação litofaciológica B pertence à zona distal do sistema fluvial, onde predominam depósitos de fluxos em lençol e canais retilíneos rasos (espraiamentos terminais fluviais). A associação litofaciológica C é definida como um sistema deltaico dominado por rios desenvolvido em momentos de subida do nível de base e formação de lagos. Por fim, a associação litofaciológica D caracteriza-se por depósitos de dunas (DU) e interdunas (IDU) recorrentes adjacentes a todas as porções do sistema fluvial distributário. O empilhamento estratigráfico revela aumento da quantidade e espessura dos depósitos eólicos em direção ao topo, indicando incremento da aridez no ambiente deposicional e expansão dos campos de dunas em direção às margens da bacia.Palavras-chave: Sistema fluvial; Clima semiárido; Interação fluvial-eólico; Elemento arquitetônico. AbstractThe Late Permian Morro Pelado Member is the upper part of the Rio do Rasto Formation of Paraná Basin and is composed of an association of fluvial, eolian and lacustrine deposits. In order to depict its facies associations and depositional elements as well as to characterize the fluvial style, a facies and architectural element analysis was carried out in the eastern outcrop belt in Santa Catarina and Paraná States, southern Brazil. Four facies associations (FA) were recognized: FA-A is interpreted as mixed-load meandering fluvial systems, with conspicuous laterally accreted macroforms, levees and floodplain fines; FA-B was deposited as terminal splays in the distal parts of the fluvial system, where sheet floods prevailed; FA-C defines a fluvial-dominated lacustrine delta formed in response to episodes of extreme flooding and rising water table in the terminal splay zone; FA-D comprises eolian dunes, wet and damp interdunes and eolian sand sheets that occur interbedded with the fluvial and lacustrine deposits marking periods of aridization in the alluvial plain. The vertical stacking pattern shows an upward increase in frequency and thickness of eolian deposits recording progressive expansion of the erg systems towards basin margins in response to progressive drying combined with high rates of accommodation and sediment supply.

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In this contribution, we present an analysis of the main faciological features of the São Jerônimo da Serra Site, related to the Morro Pelado Member of Rio do Rasto Formation (Middle/Upper Permian), from Paraná State, Brazil, integrated to its taphonomic context. The outcrop, rich in vertebrates and bivalves remains, presents a succession of red siltstones bedded with fine to medium sandstones in which three architectural elements were observed: SF (sheetflood deposits), FF (fine of flood plain) and CS (crevasse). These data, allied to the taphonomic signatures of fossils assigned to eight levels, allowed the identification of three taphofacies. The taphofacies I is characterized by preserved bones in floodplain facies, with different articulation grades and absence of any sign of transport. The taphofacies II is composed by small isolated or fragmented bones and fish scales deposited in terminal splay facies. The taphofacies III is characterized by sandy layers with bivalve shells and fish scales, preserved in crevasse-splay deposits. The obtained data shows that the studied sedimentary succession was generated on a dry trend environment, with sporadic water supply, which conditioned the fossil preservation.

The transition from the Late Paleozoic Ice Age (LPIA) to fully postglacial conditions in SW Gondwana is under increasing discussion due to either the radiometric ages of its boundary or the stratigraphic nature of this transition. The record of this transition in the Paraná Basin is found in the glacial and glacially influenced deposits of the upper Mafra and Rio do Sul Formations (upper Itararé Group) and postglacial strata of the Rio Bonito Formation (Guatá Group). Here we address the depositional architecture and stratigraphic evolution of these deposits in the Rio do Sul depocenter, eastern Paraná Basin, Brazil, the main area of subsidence in the basin during this transition in Pennsylvanian-Cisuralian time, bringing an opportunity to examine the characteristics of glacial to postglacial transition. Analyses of facies, stratigraphic logs, stratigraphic correlations, and paleocurrent dispersal trends allowed us to define three evolutionary stages. The first stage registers glacial advance from the south-southwest represented by an erosive surface and subglacial tillites. Gravitational deposits covered the tillites in response to ice retreat (upper Mafra Formation), and the Lontras Shales (lower Rio do Sul Formation) correspond to the marine maximum flooding. The second stage comprises co-genetic deepwater (Rio do Sul Formation) to shallow (Rio Bonito Formation, Triunfo Member) progradational deposits after the Lontras Shale maximum flooding. Paleocurrent data and glacially related features point to glaciated source areas located to the NE, E, and SE for the Rio do Sul depocenter during this stage. The third stage corresponds to retrogradational stacking pattern upon a fluvial subaerial unconformity (incised valley), starting with fluvio-deltaic beds (Triunfo Member), followed by fine-grained deposits of the Paraguaçu Member of Rio Bonito Formation. No features related to glacial influence characterize this third stage. As previously suggested, tectonic uplift likely drove the additional NE source and created the space that allowed the transitional contact between Rio do Sul and Rio Bonito formations in the Rio do Sul depocenter.

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