Significance of conodont data for explaining geosystem perturbations during the Middle Devonian Kačák Episode

Abstract

The present review of published data as well as the new results demonstrate the versatility of conodonts in documenting and explaining global environmental fluctuations related to the Kačák Episode (KE) in the latest Eifelian. Although the conodont zonation of the KE interval is ambiguous and requires revision, the compilation of conodont stratigraphic ranges shows their potential for a precise worldwide correlation of relevant marine strata. Conodont biofacies may serve to document environmental changes connected with KE, in particular the sealevel rise at its beginning, followed by a regressive trend. Nevertheless, the familiar Icriodus/Polygnathus ratio should be carefully applied as an indication of water depth and nearshore vs. offshore position, being controlled also by other factors, such as paleolatitude and/or climate. Oxygen isotopes in conodont apatite, studied using secondary ion mass spectrometry technique evidence a warming at the onset of KE, based on the new data from the open marine facies of the Prague Basin. At the same time, they indicated climate-controlled salinity fluctuations in the epeiric Belarusian Basin. The present investigations as well as previous results suggest caution when analyzing thermally altered conodonts which may result in biased oxygen isotope signatures. The present experience suggests the conodont colour alteration index CAI 3 as a boundary value above which the caution is necessary.