Acta Musei Moraviae

Results of sedimentological study of the Lower Miocene, chert containing gravels in the Southwestern part of the Carpathian Foredeep

Presence of chert pebbles is a typical feature of the Lower Miocene (Eggenburgian, Ottnangian) coarse grained sediments in the SW part of the Carpathian Foredeep. Cherts were found in the alluvial-fluvial deposits, in the deltaic deposits and in the shallow marine deposits. Petrological and morphometrical (shape, roundness) studies confirm the source of coarse clasts from the nearest surroundings. The source of the cherts is located in the „Krumlov Forest“. Chert clasts were eroded from the source and transported towards E, SE and SW by fluvial systems. Fluvial sediments were again eroded and redeposited during the transgression of the Lower Miocene sea. These processes were very efficient close to the margins of the basin. In this area newly eroded coarse clasts were delivered from the primary source by sea abrasion at the same time. Strong influence of wave action was recognised both on outcrops (sedimentary structures) and on pebbles. The rate of deposition played an important role, affecting the pebbles by the depositional processes.