Evolution of geochemistry and depositional settings of Early Palaeozoic siliciclastics of the Barrandian (Teplá-Barrandian Unit, Bohemian Massif, Czech Republic)

Abstract

Cambrian and Ordovician-Middle Devonian sequences of two successive Early Palaeozoic basins of the Barrandian unconformably overlie Cadomian basement in the Bohemian Massif NW interior (Tepla-Barrandian unit) which is the easternmost peri-Gondwanan remnant within the Variscides. Correlation of stratigraphy and geochemistry of the Early Palaeozoic siliciclastic rocks elucidated sediment provenances. Sandstones of the Middle Cambrian Přibram-Jince Basin were derived from a Cadomian Neoproterozoic island arc. The source area of the Ordovician shallow-marine siliciclastics of the successor Prague Basin is a dissected Cadomian orogen. Late Cambrian acid volcanics of the Barrandian and Cambrian (meta)granitoids emplaced in the W part of the Tepla-Barrandian Cadomian basement are also discernible in these sediments. Old sedimentary component increased during the Ordovician. Early Llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of Silurian transgression. Emsian siliciclastics (intercalated in the Late Silurian to Early Devonian limestone suite) presumably comprise an addition of coeval basic/ultrabasic volcaniclastics. Middle Devonian flysch-like siliciclastics indicate reappearance of Cadomian source near the Barrandian during early Variscan convergences of Armorican microplates that preceeded accretion of the Tepla-Barrandian unit within the Bohemian Massif terrane mosaic.