A Silurian volcanic island slope as an archive of mixed terrestrial and marine biota from the Prague Basin, Czech Republic: an integrated biochemostratigraphy and multiproxy analysis

The Sheinwoodian represents a critical interval in the early colonisation of terrestrial environments by vascular plants and associated cryptogamic assemblages. The Prague Basin is a historically important region, having yielded the first formally described cooksonioid plant remains. A multidisciplinary re-examination of one of Barrande's original localities, the Sedlec, Stydlé Vody Section, integrating petrography, clay mineralogy, stable-isotope and trace-element geochemistry, and macro- and microfossil data is presented herein. The studied interval consists of tuffaceous limestones and volcaniclastic interbeds of the Motol Formation, deposited on a distal volcaniclastic slope, where episodic sediment-gravity flows transported biotic material from shallower settings. The unique integration of conodont, chitinozoan, and graptolite biostratigraphic data constrains the section to the mid-Sheinwoodian. This interval encompasses the Monograptus belophorus and Cyrtograptus rigidus graptolite biozones, the middle part of the Jeppssonia sagitta rhenana Conodont Superzone, and the Cingulochitina cingulata chitinozoan Biozone. Carbonate δ13C values further confirm deposition after the early Sheinwoodian positive carbon isotope excursion (ESCIE). Both marine and terrestrial biotic signals are preserved within the Stydlé Vody slope deposits. The high diversity of dispersed spores together with associated plant remains indicates a diverse vegetation in the source area on adjacent emergent volcanic peaks, including rhyniophytes, zosterophylls, and eophytes. Jawed polychaetes (scolecodonts) are documented in detail for the first time from this stratigraphic interval and region, extending the spatial distribution of this group. Chitinozoan, conodont, and scolecodont assemblages further support palaeobiogeographic links between the Prague Basin (peri-Gondwana) and coeval successions of Baltica.