The onset of Pliocene–Early Pleistocene fluvial aggradation in the Southeastern Alpine Foreland (Velenje Basin, Slovenia) and its paleoenvironmental implications

In this study, we focused on the Pliocene–Early Pleistocene fluvial terraces in the Velenje Basin and reconstructed the morphostratigraphy, sedimentary depositional environment, provenance and age of the gravel deposits using geomorphological, sedimentological, petrographic and chronological analyses. Geomorphological mapping revealed the presence of two main river-terrace groups. The terraces in the older terrace group are severely degraded and preserved only as remnants capping high ground, while in contrast the younger group is better preserved. Detailed lithofacies analyses of four selected stratigraphic sections of the older terrace group show that the gravel was deposited in a meandering and wandering environment. The gravel consists of metamorphic, igneous, volcaniclastic, clastic and carbonate lithologies derived from the north, east and west from the Paka River catchments. To determine the timing of deposition, we performed isochron-burial dating using cosmogenic ²⁶Al and ¹⁰Be. Our new age constraints date the deposition of the older terrace group to 2.7 ± 0.3 Ma. Establishing the aggradation and incision model of the Velenje Basin documents pronounced regional tectonic uplift during the Pliocene–Early Pleistocene, which led to incision and the subsequent formation of a terrace staircase.