A SIMS zircon age for a biostratigraphically dated Upper Viséan (Asbian) bentonite in the Central-European Variscides (Bardo Unit, Polish Sudetes)

Abstract

A Lower Carboniferous platform sedimentary sequence (the Paprotnia Beds) in the Bardo Unit of the central Sudetes (NE part of the Bohemian Massif, SW Poland) is biostratigraphically well dated, based on rich macro-and micro-fossil evidence, as Late Viséan (late Asbian, crenistria, Go III a zone). The beds contain several bentonite layers, one of which was dated using the U-Pb SHRIMP method on volcanic zircons and yielded an age of 334 ± 3 Ma. This date fits well to the recently established chronostratigraphic limits of the Viséan, and is consistent with the newest isotopic age constraints of 336.5-332 Ma for the Asbian boundaries.

Post-Variscan cooling history of the central Western Sudetes (NE Bohemian Massif, Poland) constrained by apatite fission-track and zircon (U-Th)/He thermochronology

“…Franke, 1989Franke, , 2000Kroner et al, 2008;Mazur et al, 2006). While the Variscan orogeny in the Sudetes is relatively well understood and has been reasonably constrained by high temperature geochronometers (i.e., U/Pb, Pb/Pb, Lu/Hf, Sm/Nd, Rb/Sr, Ar/Ar; e.g., Anczkiewicz et al, 2007;Awdankiewicz et al, 2010;Awdankiewicz et al, 2014;Duthou et al, 1991;Kryza and Zalasiewicz, 2008;Kryza et al, 2010;Kryza et al, 2012;Kryza et al, 2014a, b;Machowiak and Armstrong, 2007;Maluski and Patočka, 1997;Marheine et al, 2002;Mazur et al, 2010;Mazur et al, 2012;Mazur et al, 2013;Oberc-Dziedzic et al, 2010;Oliver et al, 1993;Žáčková et al, 2010), the post-orogenic geodynamic events that largely occurred at low temperatures are insufficiently resolved and/or controversial (e.g. Badura et al, 2004;Dyjor, 1974Dyjor, , 1975Jarosiński et al, 2009;Piwocki, 2004;Piwocki et al, 2004;Reicherter et al, 2008;Teisseyre, 1957;Ulrych et al, 2011).…”

A waning Saxothuringian Ocean evidenced in the Famennian tephra-bearing siliceous succession of the Bardo Unit (Central Sudetes, SW Poland)

“…Only the Bardo IV site, distinguished by a tephra-bearing cherty succession, is presented in this article. Note that some Carboniferous tephras were previously studied from the northern Bardo Unit (Kryza et al, 2011); in addition, Gunia (1985;his table 3) reported "tuffite" intercalations from the Lower Devonian siliceous and clayey shales.…”

“…(Pisarzowska et al, 2020). Interestingly, the late Viséan bentonites from the autochthonous section of the Bardo Unit (Paprotnia Beds) also record explosive andesite-rhyolitic magmatic sources from a continental margin setting (Kryza et al, 2011).…”

“…Both units, despite dissimilar tectonic history and geological setting, comprise remnants of Paleozoic pre-Variscan basins containing fragments of lower Paleozoic-Devonian deep marine sediments. Conversely, the inner Bardo Basin hosted relatively shallow water sedimentation until the late Viséan (334 ± 3 Ma, Kryza et al, 2011;Paprotnia Beds). Only afterwards, sedimentation changed to hemipelagic with deposition of extensive flysch and wild-flysch series and emplacement of olistostromes (Wajsprych, 1978(Wajsprych, , 1986(Wajsprych, , 1995.…”