Influence of Uplift and Magmatism on Distribution of Quartz and Illite Cementation: Evidence from Siluro-Devonian Sandstones of the Paraná Basin, Brazil

Siluro-Devonian sandstones of the Furnas Formation in the intracratonic Paraná Basin, southern Brazil display heterogeneous distribution of quartz, kaolin and illite cementation and feldspar dissolution. Extensive dissolution and kaolinization of detrital feldspar, mica and clay pseudomatrix occurred under an eodiagenetic meteoric regime. The heterogeneous precipitation of quartz and illite is attributed to the circulation of hot fluids related to the uplift and magmatism along the regional Ponta Grossa Arch. This is supported by the high (up to 156°C) fluid inclusion homogenization temperatures in quartz overgrowths and by the intense kaolinite illitization in sandstones with maximum burial depths between 1200 and 2200 m, as well as by the high crystallinity and the K/Ar derived ages of illite that coincide with the timing of magmatism. The extensive destruction of detrital feldspar has generated diagenetic quartz arenites with poorly connected pore systems, and hence low reservoir potential. The heterogeneous patterns of diagenetic modifications displayed by the sandstones suggests that 'isochemical' diagenetic models of the system SiO₂-Al₂O₃-K₂O-H₂O have limited validity for basins with complex burial histories and magmatic activity, and may apply only to some sandstones buried deeply in rapidly subsiding basins.