High-resolution tentaculite biostratigraphy and facies development across the Early Devonian Daleje Event in the Barrandian (Bohemia): implications for global Emsian stratigraphy

Abstract

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.

Armoured test of Early Devonian Mesoconularia (Conulariida) from the Prague Basin (Czech Republic): probable adaptation to increased predation pressure

“…The lithological characteristics of the member are rather variable, due mainly to changes in the ratio of coarse-grained bioclastic (mostly crinoidal) to finer bioclastic or micritic components. The colour varies from rosy to dark red brown, depending on the content of iron oxides (Svoboda & Prantl 1948, Chlupáč et al 1979, Ferrová et al 2012. Its thickness reaches up to 15 m. The Chýnice Limestone differs in colour and fauna from the underlying, grey micritic, offshore Zlíchov Limestone, which represents the lower and, in some places, the middle part of the Emsian in the Prague Basin.…”

“…It disconformably covers the reefal Koněprusy Limestone of Pragian age (Chlupáč 1998) and was deposited following a late Pragian-early Emsian (Zlichovian) sedimentary break followed by emersion and erosion of the reef. The thickness of the Suchomasty Limestone reaches up to 30 m. The beginning of the deposition of the Suchomasty Limestone falls within the Nowakia elegans Biozone but already above the N. barrandei-elegans Subzone (see Ferrová et al 2012). The Suchomasty Limestone sequence is dominated by well-bedded, reddish and grey biomicritic and biosparitic, predominantly crinoidal limestones, indicating a shallow-water and high-energy environment (Havlíček & Kukal 1990, Chlupáč 1998.…”

“…Its thickness reaches up to 15 m. The Chýnice Limestone differs in colour and fauna from the underlying, grey micritic, offshore Zlíchov Limestone, which represents the lower and, in some places, the middle part of the Emsian in the Prague Basin. The Chýnice Limestone spans the N. barrandei and N. elegans biozones including the N. barrandei-elegans Subzone (see Ferrová et al 2012). A deepening of the basin, with onset of deposition of the more offshore Daleje Shale, follow deposition of the Chýnice Limestone.…”

“…During the last two decades several new studies focusing on brachiopods ) and gastropods (Frýda 2001;Frýda et al 2008Frýda et al , 2009 were published. Ferrová (2010) and Ferrová et al (2012), based on a bed by bed study of two sections at the classical Čeřinka locality and in the nearby Čerinka Quarry, described in detail the environmental changes across the Daleje Event and proposed a new mid-Emsian tentaculite biostratigraphy as well as a new boundary for the Dalejan (= "Upper Emsian").…”

“…The Suchomasty Limestone sequence is dominated by well-bedded, reddish and grey biomicritic and biosparitic, predominantly crinoidal limestones, indicating a shallow-water and high-energy environment (Havlíček & Kukal 1990, Chlupáč 1998. The tentaculite fauna includes the Nowakia elegans, N. cancellata, N. richteri and N. holynensis biozones (Chlupáč et al 1979(Chlupáč et al , 1986Berkyová 2004;Ferrová et al 2012). An upper Emsian age is indicated by the presence of the Polygnathus laticostatus, P. serotinus and P. costatus partitus biozones (Klapper 1977, Klapper et al 1978, Chlupáč et al 1986, Chlupáč 1998, Berkyová 2009).…”