Acta Musei Moraviae

Geochemical and petrophysical charakteristics of sediments of the Baška development at the Libhošťská hůrka

This work is focused on combined lithological, petrophysical and geochemical study of two sections (LH-1 and LH-2) at Libhošťská hůrka hill, formed by sedimentary rocks of the Baška Formation of the Baška Facies Development of the Silesian Unit of the Outer Flysch Carpathians. The main aim is interpretation of depositional environment of these sediments. The lithological description was performed on the basis of routine macroscopic field description of sedimentary rocks. Natural radioactivity of rocks was measured using field gamma-ray spectrometry. Planimetric analysis by the Gazzi-Dickinson method was applied in optical microscopy of rock thin-sections. The chemical composition of the samples was studied by energydispersive x-ray fluorescence spectrometry. Siliciclastic sediments of gravity flows, pelagic fallout and cherts were observed. Facies architecture of LH-1 section documents deposition in the central part of the submarine fan (sandy lobes). LH-2 section represents channel-fill in the proximal part of the depositional system. Provenance ternary diagrams show a source of clastic material from recycled orogen. The abundant lithic fragments of the Štramberk Limestone indicate connection with the Baška Ridge. Quartz and carbonates, in the form of both detritus and cement, are dominant components in modal composition of sandstones. This corresponds with low natural radioactivity of studied sediments. The gamma-ray spectrometric signal is mainly associated with glauconite and lithic clasts of mudstones. Si/Al and Zr/Rb ratios reflect lithological changes, indicating a shift in sedimentation to the more distal part of the deposition environment, rather than changes in sedimentary maturity. Rb/Sr ratio, low K/Al ratio values and high Si content indicate feldspar destruction and the intense supply of SiO₂ to the marine environment due to strong chemical weathering in the source area. Values of the V/Cr ratio indicate a low oxygen environment.