Changes

The Devonian package of the basin, the Paraná Group, has a maximum thickness of 800 meters and overlies the Ordovician-Silurian strata of the Rio Ivaí Group, but also can be found directly on [[basement]] rocks.  

The Devonian package of the basin, the Paraná Group, has a maximum thickness of 800 meters and overlies the Ordovician-Silurian strata of the Rio Ivaí Group, but also can be found directly on [[basement]] rocks.  

Two units constitute the Paraná Group: Furnas and Ponta Grossa Formations. The Furnas Formation is represented by a succession of white quartz sandstones, medium to coarse, with high kaolinite content and displaying cross stratification of various kinds. Near the base, are frequent conglomeratic beds up to 1 m thick. In its middle portion, dominated by sandstones of medium [[grain size]], intercalated with thinner siltstone and muscovite rich shale, emphasizing the laminated aspect of that interval. Herringbone cross-stratification also occurs.<ref name=Assine_1996 /> At the top, medium to coarse sandstones come to dominate, but also occur in very thin layers of sandstone with hummocky stratification type. Continuous increase in mudstone interbeds towards the top shows a gradational transition to the Ponta Grossa Formation.

Two units constitute the Paraná Group: Furnas and Ponta Grossa Formations. The Furnas Formation is represented by a succession of white quartz sandstones, medium to coarse, with high kaolinite content and displaying cross stratification of various kinds. Near the base, are frequent conglomeratic beds up to 1 m thick. In its middle portion, dominated by sandstones of medium [[grain size]], intercalated with thinner siltstone and muscovite rich shale, emphasizing the laminated aspect of that interval. Herringbone cross-stratification also occurs.<ref name=Assine_1996 /> At the top, medium to coarse sandstones come to dominate, but also occur in very thin layers of sandstone with hummocky stratification type. Continuous increase in [[mudstone]] interbeds towards the top shows a gradational transition to the Ponta Grossa Formation.

The Ponta Grossa Formation is represented in the lower portion, by shales c.100 meters thick, containing fine sandstone lenses with stratifications reworked by waves, and black laminated carbonaceous shale, which is an important marker for stratigraphic correlation in the subsurface and a potential generator of hydrocarbons throughout its range in the central area of the Paraná Basin. The middle portion, sandstone and siltstone alternations reflect a progradation of deltaic systems. The upper portion, predominantly mudstone, documents renewed flooding on a large scale, which caps this unit.  

The Ponta Grossa Formation is represented in the lower portion, by shales c.100 meters thick, containing fine sandstone lenses with stratifications reworked by waves, and black laminated carbonaceous shale, which is an important marker for stratigraphic correlation in the subsurface and a potential generator of hydrocarbons throughout its range in the central area of the Paraná Basin. The middle portion, sandstone and siltstone alternations reflect a progradation of deltaic systems. The upper portion, predominantly mudstone, documents renewed flooding on a large scale, which caps this unit.