Sequence stratigraphy of fluvial to shallow-marine deposits: The case of the early Permian Rio Bonito Formation, Paraná Basin, southernmost Brazil

Ricardo Maahs,Claiton Marlon Dos Santos Scherer,Juliano Küchle,Renata Dos Santos Alvarenga

doi:10.1590/2317-4889201920190059

Ricardo Maahs, Claiton Marlon Dos Santos Scherer + Show 2 more

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https://doi.org/10.1590/2317-4889201920190059

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Abstract

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 Parana Basin, southern Brazil. The study was performed based on the description of five cores, located in a small-scale area - Sao 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 Sao 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.

Highlights

IntroductionOne of the most studied units of the Paraná Basin, in southern Brazil, is the Rio Bonito Formation, due to the ubiquitous presence of coal beds and the potential of the formation as analogue for hydrocarbon reservoirs in coastal sandstones.Several works have already described the Rio Bonito Formation; its depositional environments (e.g., Schneider et al 1974, Milani 1997, Lavina & Lopes 1987, Holz 2003) and stratigraphic framework (e.g., Holz 1995, Lopes 2004, Holz et al 2010) are frequently revaluated.In the early 2000’s, several authors considered the Rio Bonito (coastal deposits) and Palermo (shallow-marine deposits) formations as coeval units (e.g., Holz et al 2006); once that shallow-marine deposits overlay coastal ones in some areas, and in others they are interfingered.Holz (2003) proposed a depositional model for the formation of a wave and tide influenced estuary evolving to a barrier-lagoon depositional system, in Candiota, southern portion
The interpretation of tidal mud and sand flats is supported by the presence of heterolithic intercalations with bidirectional tractive structures and sandstones with plant fragments (Fig. 8)
Besides that, according to Harris (1988), the filling of an estuary produces a bedform evolutionary sequence, with an initial muddy stage and a final stage with onshore sand bars. This evolutionary sequence was identified in the study area, since Transgressive system tract 1 (TST-1) presents tidal flats and some tidal sand bars and Transgressive system tract 2 (TST-2) presents mostly tidal bars (Fig. 12)

Summary

Introduction

One of the most studied units of the Paraná Basin, in southern Brazil, is the Rio Bonito Formation, due to the ubiquitous presence of coal beds and the potential of the formation as analogue for hydrocarbon reservoirs in coastal sandstones.Several works have already described the Rio Bonito Formation; its depositional environments (e.g., Schneider et al 1974, Milani 1997, Lavina & Lopes 1987, Holz 2003) and stratigraphic framework (e.g., Holz 1995, Lopes 2004, Holz et al 2010) are frequently revaluated.In the early 2000’s, several authors considered the Rio Bonito (coastal deposits) and Palermo (shallow-marine deposits) formations as coeval units (e.g., Holz et al 2006); once that shallow-marine deposits overlay coastal ones in some areas, and in others they are interfingered.Holz (2003) proposed a depositional model for the formation of a wave and tide influenced estuary evolving to a barrier-lagoon depositional system, in Candiota, southern portion. One of the most studied units of the Paraná Basin, in southern Brazil, is the Rio Bonito Formation, due to the ubiquitous presence of coal beds and the potential of the formation as analogue for hydrocarbon reservoirs in coastal sandstones. Several works have already described the Rio Bonito Formation; its depositional environments (e.g., Schneider et al 1974, Milani 1997, Lavina & Lopes 1987, Holz 2003) and stratigraphic framework (e.g., Holz 1995, Lopes 2004, Holz et al 2010) are frequently revaluated. In the early 2000’s, several authors considered the Rio Bonito (coastal deposits) and Palermo (shallow-marine deposits) formations as coeval units (e.g., Holz et al 2006); once that shallow-marine deposits overlay coastal ones in some areas, and in others they are interfingered.

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