High-resolution tentaculite biostratigraphy and facies development across the Early Devonian Daleje Event in the Barrandian (Bohemia): implications for global Emsian stratigraphy
Abstrakt
The long-term activities of the International Subcommission on Devonian Stratigraphy have been focused on the division of the Emsian into two new substages. The different stratigraphic levels, close to the Daleje Event, have mostly been discussed as their boundary.
The latter event was first recognized in the Barrandian and defined as a bioevent, connected with a pronounced transgression. Its present conception has been inferred from studies of its appearance in deeper environments, with deposition of the calcareous Daleje Shale.
We analysed its appearance in shallower environments, with predominantly carbonate sedimentation, using precise qualitative and quantitative biostratigraphic, paleoecological, and sedimentological methods. Our data revealed that the mid-Emsian had a more complex transgression-regression history than previously described.
Evaluation of the stratigraphic distribution of more than 1250 newly collected dacryoconarid shells has resulted in the proposal of a new tentaculite biozonation, providing a much higher stratigraphic resolution than the existing biozonations, which are based on goniatites and conodonts. Quantitative analysis of the newly gathered paleoecological data suggests a distinct faunal turnover at the level of the first occurrence of the dacryoconarid tentaculite Nowakia elegans.
In addition, our study revealed that the Daleje transgression (and thus the Daleje Event) started at the same time, and that it was preceded by a distinct regression. For these reasons, we propose the first occurrence of the worldwide and easily determinable dacryoconarid Nowakia elegans as a biostratigraphic indicator of the boundary level for the new Emsian substages.