Lower Cretaceous belemnite associations from the Rychaltice locality and the disintegration of the Baška Ridge (the Silesian Unit, Outer Western Carpathians, Czech Republic)
Article PDFLower Cretaceous belemnite associations from the Rychaltice locality and the disintegration of the Baška Ridge (the Silesian Unit, Outer Western Carpathians, Czech Republic)
An approximately 200 m long road-cut near the village of Rychaltice uncovered the exposure with Lower Cretaceous sedimentary sequence of the Baška Subunit of the Silesian Nappe at the contact with Paleogene deposits of the Subsilesian Nappe (Outer Western Carpathians). At the base of the Silesian Nappe tectonical melange with blocks, a lenticular olistostrome and pebbles of Štramberk-type limestones occur at the contact zone of both nappes. Weathered and partially reworked belemnite rostra come from the weathered dark grey unstratified mudrocks, in a section of only several meters thick. The collection of more than one hundred incomplete and small-sized rostra of belemnites is the subject of a taxonomic and stratigraphic evaluation. Despite the unfavourably preservation of the rostra, it was possible to identify at least 4 taxa, which indicate the stratigraphic range of almost the entire Lower and the base of Upper Cretaceous series. Among these, the oldest fragments are of Pseudobelus ex gr. bipartitus, which show a broad stratigraphic range from the late Berriasian to the early late Hauterivian. In addition, there is a small (probably juvenile) specimen of Duvalia ex gr. binervia of the late Valanginian – earliest Hauterivian age. The rare species mentioned above are accompanied by the occurrence of Parahibolites tourtiae and the abundant occurrence of Neohibolites ex gr. minimus – ultimus. The latter association indicates a (late) middle Albian to the early Cenomanian age. Additionally, to the stratigraphic spectrum of belemnites (late Berriasian – early Cenomanian), the finding of a single valve of the aptychus Punctaptychus cf. punctatus gives the evidence for even older material present, i.e. Tithonian to Berriasian. Determined belemnites and aptychus, indicate the Berriasian to the early Cenomanian age of the conglomerate deposits of Chlebovice facies (Baška Development).
Zdeněk Vašíček, Institute of Geonics of the Czech Academy of Sciences, Studentská 1768/9, CZ-70800 Ostrava-Poruba; email: Zdenek.Vasicek@ugn.cas.cz