Kenozoické sedimenty v lomu Předklášteří u Tišnova

Abstract

In the multi-level quarry Předklášteří near Tišnov exploiting medium-grained biotite metagranite of the Brunovistulicum, up to 30 m thick unconsolidated sediments, were studied recently at the top of excavation. These sediments are exposed at the two top quarry levels. During the exploration work in 1965, these sediments were not encountered, because today’s quarry mining area has already exceeded the original considerations about the extent of mining.The altitude of the erosive base of these fluvial or deltaic sediments 370–375 m indicates their pre-Quaternary age. Our research was focussed on the Lower Miocene part of the sediments tentatively considered as lake, delta or river sediments. Sediments were studied by sedimentological, petrographic, mineralogical, geochemical and paleontological methods. Preliminary results from overlaying Quaternary sediments did not allow definite stratigraphical interpretation.Geochemical analyses of silty clays to claystones were compared with the occurrences of similar sediments from Brno and its surroundings (Kamechy, Kohoutovice, Obřany, Svinošice). These analyses proved that the sediments underwent a short transport of several kilometres and could be derived from weathering residues of the rocks forming the surrounding Brunovistulicum.Our research has confirmed the affiliation of sediments in top of the sequence to the Pleistocene colluvial deposits. Sediments found in the lower part of the layered sequence, trapped along the fault of the E–W direction, were assigned stratigraphically to the Lower Miocene (Ottnangian).