Heavy mineral suites in Oligocene-Miocene sediments (Fore-Sudetic Monocline, SW Poland): Provenance signals versus weathering alteration

Abstract

The paper describes the diversity of the heavy mineral suites in the Oligocene and Miocene sediments that were deposited in the foreland of the Sudetic part of the Bohemian Massif. The observed mineral variability is the result not only of changes in sediment transport directions, but also of chemical weathering and hydrodynamic sorting of the minerals by density. All the heavy mineral assemblages lack olivines, pyroxenes and amphiboles, i.e. chemically unstable minerals. Moreover, the terrestrial sediments are impoverished in non-resistant heavy minerals in comparison to the marine ones. The central and eastern part of the Fore-Sudetic Block and, from the Middle Miocene, a part of what are now the Sudetes Mts. constituted the main source areas supplying detrital material to the Fore-Sudetic Monocline. Generally, the heavy minerals document a gradual lowering of the western fragment of the Meta-Carpathian Arch separating the North-West European Basin from the Paratethys, and a distinct shift in source areas delivering detrital material to the basin in the Middle Miocene. Furthermore, a pyroclastic origin for some heavy minerals from the sands/silts of the Middle Miocene Mużaków formation is suggested.