Multi-proxy provenance study of sandstones from the northern Bohemian Cretaceous Basin (Germany, Czechia) focused on tourmaline, rutile and garnet

The Kreibitz-Zittau area (northern margin of the Bohemian Massif, Czech-German border region) exposes a ∼1000-m-thick Cenomanian–middle Coniacian succession of quartz arenites with high compositional but low textural maturity. Translucent heavy minerals are almost exclusively composed of zircon, tourmaline and rutile (Ø-ZTR maturity index of 91) with tourmaline predominating (average of 60 %). Zr-in-rutile temperatures document upper amphibolite-eclogite to granulite facies between 700 and 930 °C. Cr/Nb discrimination of rutile and geochemistry of tourmaline indicate that >95 % of these grains originate from Al-rich and Fe–Mg-poor metapelites. U–Pb-ages of detrital rutile show a distinct peak at 320–330 Ma. If present, garnets of the almandine–pyrope series are dominant. The 95 % predominance of Variscan U–Pb rutile ages in all samples and the high/ultrahigh temperatures of metamorphism exclude the Neoproterozoic greywackes and granitoids of the Lusatian Massif and the granitoids of the Jizera–Krkonoše Massif in the northeast as sources. Potential proto source rocks were high-grade metamorphic rocks similar to those today exposed within the gneissic-migmatitic Góry Sowie Massif, ca. 120 km east of the depositional area. Since the late Devonian, this massif was uplifted, reaching the surface in late Carboniferous times. Consequently, the widespread Permo–Carboniferous Variscan molasse is the major sediment source for the Cretaceous sandstones, which thus were deposited during at least their 2nd sedimentary cycle. The study shows that integrated approaches combining careful petrography, heavy mineral analyses, mineral-specific geochemistry and thermometry as well as U–Pb age dating with high-resolution stratigraphy are suited to solve complex provenance puzzles.