Environmental and biotic changes in subtropical isolated carbonate platforms during the Late Silurian Kozlowskii Event, Prague Basin

The Kozlowskii Event extinction in the Prague Basin is not prominent in number of extinct taxa among Ludfordian extinctions, but by its short duration and changes in community structure in both nektonic, pelagic and benthic faunas of different depth zones. The number of taxa going extinct is relatively low because some sensitive benthic and nectobenthic organisms (e.g., trilobites, cephalopods, gastropods, brachiopods) disappeared already at the base of the Neocucullograptus kozlowskii Zone contemporaneous with the beginning of a sea level highstand. The Kozlowskii Event includes two phases of extinction coinciding with two erosional sequence boundaries. The event also coincides with climatic changes and alterations of the ocean current regime. Sedimentary facies indicate that the first phase of extinction in the upper N. kozlowskii Zone took place during a sea level highstand situation. A lowstand with associated reduction in current activity occurred during the second phase of extinction in the lowermost Pseudomonoclimacis latilobus Zone. Recovery was completed in the upper P. latilobus Zone. The Kozlowskii Event is in the Prague Basin is accompanied by an abrupt change of benthic and pelagic communities and by immigrations from Baltica, Avalonia and Laurentia. The initial delta C-13 excursion correlates in the Prague Basin with the uppermost N. kozlowskii Zone after the last appearance datum of the conodont Polygnathoides siluricus.