Heterogeneous generation and evolution of diagenetic quartzarenites in the Silurian-Devonian Furnas Formation of the Paraná Basin, southern Brazil

Abstract

Silurian-Devonian sandstones of the Furnas Formation in the intracratonic Paraná Basin, southern Brazil, display strongly heterogeneous distribution of quartz, kaolinite and illite authigenesis. The sandstones were affected by extensive dissolution/kaolinization of detrital felsdpar, mica and clay under an eodiagenetic meteoric regime. Circulation of hot fluids through fractures related to the uplift and magmatism along the regional Ponta Grossa Arch promoted heterogeneous kaolinite and feldspar illitization and quartz cementation. This is supported by intense illitization of kaolinite at shallow depths, by K Ar dating of the illite, whose age coincides with the magmatism, and by high fluid inclusion homogenization temperatures in quartz overgrowths from outcrop-samples. The progressive destruction of feldspar generated diagenetic quartzarenites with poorly connected pore systems and low reservoir potential. Evidence yielded by this study suggests that the application of simplified ‘isochemical’ models of diagenetic processes within the system SiO 2Al 2O 3K 2OH 2O may have very limited validity, applying basically to the deep-burial mesodiagenesis of some sandstones in rapidly subsiding basins.