Mineralogical, penological and geochemical characteristics of the süiciclastic rock types of Boda Siltstone Formation

Abstract

In this paper, results of mineralogical, petrologieal and geochemical studies of süiciclastic sedimentary
rock types (claystone, siltstone, sandstone and albitolite) of the Upper Permian Boda Siltstone Formation
(BSF) from southern Transdanubia (Mecsek Mountains, SW Hungary) are presented. The claystone
samples generally have higher illite±muscovite, haematite and chlorite contents relative to the albitolite,
siltstone and sandstone samples. In contrast, the BSF rock types with coarser grain-size have higher
albite, quarz and carbonate contents relative to the claystone samples. Degree of the diagenetic
albitisation of the detrital feldspars and carbonate cementation rate are higher in the siltstone and
sandstone samples, corresponding to their higher primary porosity, than those in the claystone samples.
Additionally, geochemistry of the studied BSF lithotypes also reflects the effect of the diagenetic
processes during albitisation. The siltstone and sandstone samples have relatively high Si0 2 , Na 2 0 , CaO,
MnO, Sr and Ba contents. On the other hand, the claystone samples have high A1 2 0 3 , Fe 2Ó3 , MgO, K 2 0
and Rb contents reflecting their higher phyllosilicate and haematite contents.
In the sandstone samples of the BSF, the presence of abundant felsic volcanic rock fragments suggests
a provenance from the Permian Gyűrűfű Rhyolite Formation. Metamorphic source components might
have been derived from the uplifted basement rocks. A relatively felsic provenance area is also
supported by the rare earth element (REE) contents of the claystone and sandstone samples showing
REE patterns typical of continentally-derived sediments. The presence of intermediate-basic volcanic
rock fragments suggests a mafic source component of the provenance area of the BSF in inconsiderable
amounts.