Trilobite biostratigraphy of the Králův Dvůr Formation (upper Katian, Prague Basin, Czech Republic): global faunal changes or facies-related distribution?
Eight trilobite associations and sub-associations have been distinguished in the late Katian Králův Dvůr Formation. Spatial distribution of these associations reflects lithology but their succession was dictated also by global climatic changes and palaeogeographical positioning. Locally developed “Podolí Ore Horizon” trilobite association contains low-diversity but specific forms showing survivals from the underlying Bohdalec Formation combined with the late Katian taxa (Chlustinia, Duftonia, Onnia, etc.). The Amphitryon – Kloucekia Association is newly established for the lower two thirds of the formation. It is characterized by abundant benthic scavenger-predators accompanied by filter feeders and common pelagic/nektic predators. Within Amphitryon –Kloucekia Association can be distinguished four sub-Association 1) the newly established Onnia ultima sub-Association is characterized by a dominance of Onnia and Flexicalymene; it is developed at the lowermost levels of the formation, 2) the deeper-water Nankinolithus granulatus sub-Association (originally established as horizon), 3) rather shallow-water, brachiopod-dominated Dedzetina-Tretaspis sub-Association with rare trilobites and 4) the trilobite-dominated Tretaspis anderssonni sub-Association (originally horizon). Last three sub-associations are considered as rather facies-related, with limited stratigraphical applicability only. Impure bioclastic limestone below top of the formation contains a rich shallow- and temperate-water Marekolithus kosoviensis Association, which better corresponds with the original horizon concept. This association is dominated by small benthic scavenger-predator trilobites, which are associated by the filter feeder Marekolithus. The Mucronaspis Association of medium-sized scavenger-predators is characteristic for the uppermost portion of formation and persisted till the early onset of the glaciation at the base of Hirnantian. Minute detritus feeders are rare but present in all the above-discussed associations excluding the last one.