Rio Do Rasto Formation Research Articles

Temnospondyl remains from the Late Permian Rio do Rasto Formation (Paraná Basin) of Brazil

Several fragmentary and isolated materials are described from the Morro Pelado Member of the Late Permian Rio do Rasto Formation, that were found at PR-090, near Sao Jeronimo da Serra town (Parana State). The materials consist of three mandibular fragments, six vertebral elements, a rib fragment, an interclavicle, a fragment of a probable scapulocoracoid and isolated proximal ends of an ulna and a femur. All the materials come from the same outcrop and the same fossiliferous horizon, without any indication of having belonged to the same individual. Although the anatomical features of most of the materials suggest they could be related to temnospondyl amphibians, their fragmentary nature and the absence of cranial specimens does not allow a more precise taxonomic identification. However, as fossil tetrapods are useful for biostratigraphic purposes, specially for the Permian-Triassic interval, the new discoveries in the Rio do Rasto Formation could provide additional support for a correlation of Permian sediments of Parana Basin with the Pristerognathus, Tropidostoma and Cistecephalus Assemblage Zones of the Karoo Basin as previous studies have suggested. Although, new material and a more precise taxonomic identification could corroborate this correlation. RESUMO - Diversos materiais fragmentados e isolados sao descritos provenientes do Membro Morro Pelado do Permiano Superior da Formacao Rio do Rasto, encontrados na PR-090, proximo a cidade de Sao Jeronimo da Serra (Estado do Parana). Os materiais consistem de tres fragmentos mandibulares, seis elementos vertebrais, um fragmento de costela, uma interclavicula, o fragmento de um provavel escapulo-coracoide, e fragmentos das porcoes proximais de uma ulna e de um femur. Todos os materiais foram coletados no mesmo afloramento e no mesmo horizonte fossilifero, sem sinal de terem pertencido ao mesmo individuo. Apesar das caracteristicas anatomicas da maior parte dos materiais sugerirem que possam estar relacionadas a anfibios temnospondilos, sua natureza fragmentada e a ausencia de especimes cranianos nao permite uma identificacao taxonomica mais precisa. Entretanto, como tetrapodes fosseis sao muito uteis para propositos bioestratigraficos, especial- mente para o intervalo Permiano-Triassico, as novas descobertas na Formacao Rio do Rasto podem fornecer suportes adicionais para a correlacao dos sedimentos permianos da bacia do Parana com as zonas de assembleia de Pristerognathus, Tropidostoma e Cistecephalus da bacia de Karoo, como havia sido sugerido em estudos anteriores. Entretanto, novos materiais e tambem uma identificacao taxonomica mais precisa podera corroborar essa correlacao. Palavras-chave: bioestratigrafia, Permiano Superior, Formacao Rio do Rasto, Temnospondyli.

Evolução sedimentar da Formação Rio do Rasto (Permo-Triássico da Bacia do Paraná) na porção centro sul do estado de Santa Catarina, Brasil

Between the Late Carboniferous and the Early Triassic, the south portion of the Gondwana Supercontinent witnessed the development of intracratonic basins related with the coeval Sanrafaelic Orogeny. The continuous subsidence and consequent generation accommodation space resulted in the formation of a large confined water body and the accumulation of a transgressive-regressive sequence between the Late Permian and the Early Triassic. The progradational nature of the upper portion of this sequence, represented by de Rio do Rasto e Piramboia formations, culminated with the complete filling of the water body. In the south-eastern portion of Santa Catarina State (Southern Brazil), the Rio do Rasto Formation overlies the Teresina formation and is overlain by the Piramboia formation, both contacts being characterized by lithological transition. The lower portion of the Rio do Rasto Formation is characterized by architectural elements deposited in offshore environments subject to storm action. A marked change of the color of the pelitic facies, from gray to red and purple occurs at the top of the unit. At this stratigraphic level, there is also a predominance of deltaic and eolian architectural elements. The intercalation of nearshore and offshore architectural elements can be explained by the strong auto cyclic character expected in deltaic depositional systems and by the variation of relative rates of base-level rise. The occurrence of eolian architectural elements interbedded with subaquatically deposited sediments on the second third of the unit can be considered an evidence of continentalization to the top, materialized as the transition to the Piramboia desert system.