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A complex depositional and tectonic history of Permo-Triassic intra-Pangea red beds in the Bohemian Massif as recorded by detrital zircon geochronology and magnetic fabric

The late Carboniferous–Early Triassic Krkonoše Piedmont Basin in the northern Bohemian Massif was initiated as a fault-controlled basin during the waning stages of the Variscan orogeny and its transition to an intra-plate setting. The basin was filled with 9 formations of mostly red beds with a total thickness more than 2000 m, deposition was accompanied by extensive volcanic activity dominated by andesitic lava flows and ash-flow and ash-fall tuffs. The U–Pb detrital zircon geochronology on 17 samples taken up-section across the basin stratigraphy points to local as well as distant sources of detritus derived predominantly from the nearby Saxothuringian and Teplá–Barrandian units, with Archean–Paleoproterozoic, Ediacaran, Cambro-Ordovician, Late Devonian and middle–late Carboniferous age peaks. Furthermore, magnetic fabric of the red beds was analysed at 29 sampling sites using the anisotropy of magnetic susceptibility (AMS) method in order to understand both the syn- and post-depositional history of the basin. Five different fabric types were detected across the basin and interpreted in terms of random orientation of magnetic grains due to turbulent flow (Type 1), strong alignment of magnetic minerals representing depositional fabric and recording paleocurrent directions (Type 2), superposition of compaction strain onto pre-existing depositional fabric (Type 3), tectonic fabric formed due to small increments of regional strain (Type 4), and an anomalous, mineralogy controlled inverse fabric (Type 5). Altogether the detrital zircon ages and multiple magnetic fabrics reveal a long term and complex sedimentary and post-sedimentary evolution and inversion of the basin in the Pangea interior.

Details

Author
Jiří Žák1, Karel Martínek1, Filip Tomek1, Martin Svojtka2, František Vacek3, Kryštof Verner3, Roland Nádaskay3
Institutionen
1Institute of Geology and Paleontology, Faculty of Science, Charles University, Prague, Czech Republic; 2Institute of Geology of the Czech Academy of Sciences, Prague, Czech Republic; 3Czech Geological Survey, Prague, Czech Republic
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/f1vz-9d68