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This unit, the oldest identified in the Paraná Basin, rests directly on the various areas of the basement. Its top is marked by a regional unconformity surface that juxtaposes the Early Silurian strata of the upper Rio Group Ivaí when it displays its complete record into the Lower Devonian, at the base of the Furnas Formation.

This unit, the oldest identified in the Paraná Basin, rests directly on the various areas of the basement. Its top is marked by a regional unconformity surface that juxtaposes the Early Silurian strata of the upper Rio Group Ivaí when it displays its complete record into the Lower Devonian, at the base of the Furnas Formation.

Three units constitute the Rio Ivaí Group: Alto das Garças, Iapó and Vila Maria Formations (Assine et al., 1996)<ref name=Assine_1996>ASSINE, M. L. Aspectos da estratigrafia das sequências pré-carboníferas da Bacia do Paraná no Brasil. 1996. 207 p. Tese (Doutorado) - Universidade de São Paulo, São Paulo, 1996.</ref>. The Alto das Garças Formation, with a maximum thickness of 300 meters, is essentially sand dominated and may include a basal quartzose conglomerate, passing to conglomeratic sandstones with cross stratification. The upper portion of the unit is represented by an increase in the amount of silt and clay and reddish coloration.

Three units constitute the Rio Ivaí Group: Alto das Garças, Iapó and Vila Maria Formations.<ref name=Assine_1996>Assine, M. L., 1996, Aspectos da estratigrafia das sequências pré-carboníferas da Bacia do Paraná no Brasil. 1996. 207 p. Tese (Doutorado) - Universidade de São Paulo, São Paulo.</ref>. The Alto das Garças Formation, with a maximum thickness of 300 meters, is essentially sand dominated and may include a basal quartzose conglomerate, passing to conglomeratic sandstones with cross stratification. The upper portion of the unit is represented by an increase in the amount of silt and clay and reddish coloration.

The Iapó Formation consists of diamictites of different colors, with silty-sandy matrix and varied nature of clasts. The Vila Maria Formation is comprised of fossiliferous pelites representing the most important stratigraphic mark of all Supersequence Rio Ivaí. Are generally red colored, micaceous and ferruginous appearance, but locally dark gray and quite fossiliferous. In turn, the sandstones and siltstones of the upper portion display hummocky cross-bedding and contraction desiccation cracks.  

The Iapó Formation consists of diamictites of different colors, with silty-sandy matrix and varied nature of clasts. The Vila Maria Formation is comprised of fossiliferous pelites representing the most important stratigraphic mark of all Supersequence Rio Ivaí. Are generally red colored, micaceous and ferruginous appearance, but locally dark gray and quite fossiliferous. In turn, the sandstones and siltstones of the upper portion display hummocky cross-bedding and contraction desiccation cracks.