Facies development, depositional settings and sequence stratigraphy across the Ordovician–Silurian boundary: a new perspective from the Barrandian area of the Czech Republic

Abstract

The Hirnantian and Llandovery sedimentary succession of the Barrandian area has been assigned to middle and outer clastic-shelf depositional settings, respectively. Deposition was influenced by the remote Gondwanan glaciation and subsequent, long-persisting, post-glacial anoxia triggered by a current-driven upwelling system. High-resolution graptolite stratigraphy, based upon 19 formally defined biozones-largely interval zones-and five subzones, enabled a detailed correlation between 42 surface sections and boreholes, and enabled linking of the sedimentary record, graptoloid fauna dynamics, organic-content fluctuations and spectral gamma-ray curves. The Hirnantian and Llandovery succession has been subdivided into four biostratigraphically dated third-order sequences (units 1-4). Time-spatial facies distribution recorded early and late Hirnantian glacio-eustatic sea-level lowstands separated by a remarkable mid-Hirnantian rise in sea-level. A major part of the post-glacial sea-level rise took place within the late Hirnantian. The highstand of Unit 2 is apparently at the base of the Silurian succession. Short-term relative sea-level drawdown and a third-order sequence boundary followed in the early Rhuddanian upper acuminatus Zone. Early Aeronian and late Telychian sea-level highstands and late Aeronian drawdown of likely eustatic origin belong to units 3 and 4. Sea-level rise culminated in the late Telychian, which may also be considered as a highstand episode of a second-order Hirnantian-early Silurian cycle. Facies and sequence-stratigraphic analysis supports recent interpretations on nappe structures in the core part of the Ordovician-Middle Devonian Prague Synform of the Barrandian.

Odontopleurid trilobites of the Katian/Hirnantian boundary interval in the Prague Basin (Bohemia)

“…These layers contain a different low-diversity fauna, dominated by ostracods, machaeridians, few orthid brachiopods, and especially the trilobite Mucronaspis grandis (Barrande, 1852). The presence of brachiopods Kinnella kielanae (Temple, 1965) and Hirnantia sagittifera (M'Coy, 1851) and graptolite Metabolograptus ojsuensis (Koren & Mikhaylova, 1980) confirms the Hirnantian age of this claystone (Štorch 2006(Štorch , Mergl 2011a.…”

Trace element variations as a proxy for reconstruction of palaeoenvironmental changes during the Late Aeronian faunal and carbon isotope perturbations: new data from the peri-Gondwanan region

“…Depositional set tings, bi otic and en vi ron men tal changes, and stra tig ra phy have been studied in the Lower Si lu rian suc ces sion of the Prague Synform by Bouèek (1953), Køíž (1975Køíž ( , 1992, Štorch and Pašava (1989), Štorch (2006), Štorch and Frýda (2012), Frýda and Štorch (2014) and oth ers. High-res o lu tion cor re la tion of lithological changes re corded in the Lower Si lu rian suc ces sion with en viron men tally driven, world-wide changes is en abled by highly de vel oped graptolite biostratigraphy (Bouèek, 1953;Štorch, 1994, 2006 and car bon iso tope geo chem is try Frýdová, 2014 2016;Frýda and Štorch, 2014;. The geo chem is try of Lower Si lu rian se quences in the Prague Synform was first stud ied by Marešová (1973), fol lowed by Lepka et al (1984).…”

Hirnantian (latest Ordovician) glaciations and their consequences for the Oslo Region, Norway, with a revised lithostratigraphy for the Langøyene Formation in the inner Oslofjorden area

“…sea-level fluctuations on many continents at different palaeolatitudinal positions (Kaljo et al, 2001;Bergström et al, 2006;Brenchley et al, 2006;Štorch, 2006;Johnson & Baarli, 2007;Davies et al, 2009;Ghienne et al, 2014;Demski et al, 2015;Kröger et al, 2015). The Oslo Region was situated in a subtropical position during the Ordovician (Torsvik & Cocks, 2013), and the effects of sea-level changes are also recorded there.…”