VRTBY ICHNORODU GASTROCHAENOLITES JAKOŽTO ŽIVOTNÍ PROSTOR MLŽŮ Z LOKALITY BORAČ-PODOLÍ (KARPATSKÁ PŘEDHLUBEŇ, ČESKÁ REPUBLIKA)

Abstract

In 2015 the locality Borač-Podolí was newly examined. The locality is situated 8 km NW from the town of Tišnov. A large amount of shallow-water fossils of middle Miocene (Badenian) age was collected. The state of preservation of the material enabled us bivalve borings of ichnogenus Gastrochaenolites which were bored into colonies of hermatype corals and other calcareous hard substrates. In some of these borings, bivalves were found in situ. The borings were determined as Gastrochaenolites isp., Gastrochaenolites orbicularis, Gastrochaenolites lapidicus, Gastrochaenolites dijugus and Gastrochaenolites torpedo. The in situ bivalves were determined as Gastrochaena cf. intermedia, Rocellaria cf. dubia, Hiatella arctica and Cardita calyculata. The first three species probably represent primary borers while Cardita calyculata is probably a secondary user (squatter). Based on an analysis of fossil material, we can assume that borings were created aft er the death of corals during the repeated transport of these bioclasts. It led to colonizing of the whole surface of coral bioclasts. The bioclasts were then moved to deeper water. Transport to water with clay sedimentation enabled the preservation of the bivalves in situ in borings.