Abstract This study presents new sedimentology data and attempts to understand coastal processes, sedimentary dynamics and stratigraphic patterns of the Rio Bonito Formation (early Permian) in Paraná Basin, southern Brazil. The study was performed based on the description of five cores, located in a small-scale area - São Gabriel City - in Rio Grande do Sul State, southern Brazil. Eighteen facies were described and grouped into nine facies associations. Later, these facies associations were then grouped into three depositional systems: fluvial, tide-dominated estuary and wave-dominated shallow-marine depositional systems. A paleoenvironmental evolution is proposed using three block diagrams showing the paleoenvironmental stage (S1, S2, and S3). S1 contains the oldest part of the sedimentary record with predominance of fluvial system deposits, S2 comprises dominantly estuarine system deposits, and S3 is mostly composed of shallow-marine deposits. Stratigraphic framework showed a general retrogradacional tendency, with thickness variations along the systems tracts that allowed for the construction of a curve of accommodation changes to the Rio Bonito Formation in the region of São Gabriel during the early Permian. This study contributes to a better understanding of the fluvial discharges, tidal and oscillatory (wave) currents and their interactions and dominances along stratigraphic records of coastal deposits.

Resumo: O Gráben de Camamu corresponde à extremidade sul de um sistema de grábens conectados limitado pelo sistema de falhas de Maragogipe. Evidências estruturais e estratigráficas indicam que os depósitos deste gráben foram controlados por tectônica rifte. Foram reconhecidas duas sequências deposicionais. A base da Sequência I é composta por leques aluviais provenientes da margem leste, depositados durante a rotação do embasamento. Estes leques eram dominados por fluxos gravitacionais e por canais entrelaçados rasos com dunas eólicas subordinadas. A drenagem principal era caracterizada por canais entrelaçados profundos que fluíam para ENE, transpassando os altos estruturais da margem leste. O padrão agradacional e as características arquiteturais do sistema fluvial caracterizam um trato de sistemas de baixa acomodação. Sobre estes depósitos se estabelece um sistema fluvial distributário, caracterizado por canais fluviais de carga mista que perdem grande parte de sua energia em direção as suas porções distais, onde dominam inundações em lençol de baixa energia em uma planície de inundação com lagos efêmeros. O padrão de empilhamento retrogradacional é atribuído ao aumento nas taxas de subsidência tectônica. A Sequência II marca um rápido avanço do sistema distributário após uma erosão generalizada da planície de inundação causada pela queda no nível de base. Esta sequência é composta por canais fluviais de carga de fundo com preenchimento multiepisódico, que se intercalam com depósitos de inundações em lençol arenosas e dunas eólicas subordinadas. A arquitetura fluvial e o padrão agradacional indicam condições de baixas taxas de acomodação.

Abstract: Camamu Graben corresponds to the southern portion of a connected graben system bounded by Margogipe’s Fault System. Structural and stratigraphic evidences reveal that the deposits within this graben were controlled by rift related tectonics. Stratigraphic analysis allowed the recognition of two unconformity-bounded sequences. The base of Sequence I is composed by alluvial fans coming from the east margin and deposited during basement rotation. These systems were dominated by gravitational flow or braided channels, with subordinated aeolian dunes. The main drainage was characterized by a deep braided channel system, which flowed eastward, transposing the structural high of the east margin. The agradational stacking pattern and the fluvial architectural characteristics marks a low accommodation systems tract. Above these deposits takes place a distributary fluvial system, characterized by mixed load rivers and in its distal portion by sheet floods in a muddy flood plain with ephemeral lakes. The retrogradational stacking pattern is attributed to an increase on subsidence rates. Sequence II marks the ongoing of the distributary system basinward after a generalized erosion of theflood plain deposits caused by a base level fall. This sequence is composed by bed load channels interlayered with sandy sheet floods and subordinated aeolian dunes. The fluvial architecture and the agradational stacking pattern suggest low accommodation conditions.