In search of Silurian/Devonian boundary conodont markers in carbonate environments of the Prague Synform (Czech Republic)

Abstract

Conodonts from two of the most representative sections in the Prague Synform were studied in search of alternative biostratigraphic markers of the Silurian/Devonian boundary. The Na Požárech and Praha-Radotín sections, with contrasting lithologies, were chosen to study changes in conodont faunas in relation to different carbonate facies – i.e., shallower- and deeper-water carbonates around the Silurian/Devonian boundary in the type area. Apart from icriodontids, the differences in bathymetry were also expected to affect the diversity of taxa of the family Spathognathodontidae, which is generally the most abundant and the most tolerant clade found in different carbonate environments at this stratigraphic level. Although the Scyphocrinites Horizon is developed at both study localities, the microfacies analysis confirmed significant differences in depositional environments at around the Silurian/Devonian boundary. Abundant conodont material from the two sections (more than one thousand elements) showed a high diversity and disparity in both the Spathognathodontidae and Icriodontidae. Altogether, 18 taxa were identified, but many forms still require a formal description. A new spathognathodontid taxon, Zieglerodina petrea sp. nov., described herein, is easily distinguishable because of its distinct morphology in denticulation of the blade, and its first occurrence is just above the base of the Devonian in both sections. It also has been identified in conodont collections from Morocco and the Carnic Alps, as such its biostratigraphic significance can be extended to peri-Gondwana. Although the stratigraphic occurrence and global significance of this promising conodont taxon still has to be tested in other areas, current data suggest it might have a great potential for identifying the base of the Devonian in sections where critical graptolite and icriodontid taxa are missing.