Palaeomagnetic age constraints indicate post-Variscan orgin of massive breccia in Wietrznia Quarry (Holy Cross Mountains, Central Poland)

Abstract

Palaeomagnetic study has been carried out to resolve the controversy over the age and origin of the massive breccia body exposed in Wietrznia Quarry in the Holy Cross Mountains. The breccia studied consists of variously sized angular fragments of Frasnian and Fammenian limestone and shale infilling a palaeodepression within Frasnian limestone. For this purpose, the conglomerate test has been applied that enables determination of the relative age of remanence components and formation of the breccia. Palaeomagnetic analysis of breccia clasts reveals the presence of two characteristic components of magnetization. The observed components are akin to those previously described from in situ rocks at Wietrznia Quarry and from other Devonian carbonates from the Holy Cross Mountains. Such components have been interpreted as early synfolding and postfolding overprints of Viséan and Early Permian age. The palaeomagnetic conglomerate test performed in this study are positive results, indicating that the breccia postdates both components. This implies that the breccia is not of synsedimentary character and postdates Variscan deformation.