Origin and timing of palaeovalleys in the Carpathian Foredeep basement (Sędziszów Małopolski-Rzeszów area; SE Poland) in the light of palynological studies.

The northern margin of the Carpathian basins and their closest foreland are not preserved nowadays being partly destroyed by the subduction processes, and partly hidden under several kilometres thick cover of overthrusted Carpathian nappes and autochthonous Miocene deposits. Seismic data show along the whole arch of the Carpathian orogene lowered areas that form elongated structures in the basement, approximately perpendicular to the front of the overthrust. These structures were interpreted as palaeovalleys incised in an uplifted basin margin prior to the overthrust of folded Carpathian nappes. Studies of their sedimentary sequences, for these profiles located at the depths accessible by the boreholes, have yielded ambiguous results so far. One such a palaeovalley filled with initial stage deposits was detected in the vicinity of Rzeszów, SE Poland. Organic-rich, fine-grained deposits from the middle part of this sequence yielded palynomorphs allowing their dating. We present timing of the Rzeszów palaeovalley formation based on palynological interpretations and comparison with regional geology of the Carpathian domain. • Palaeovalley origin reflects orographic differences between foreland and flysch basins. • Fine-grained fill of palaeovalley studied yielded sporomorphs allowing its timing. • Late Cretaceous palynomorphs date beginning of palaeovalley incision. • Oligocene lacustrine-marshy environment ceased palaeovalley fulfilment. • Palaeovalley timing correlates with increased chaotic deposits accumulation in Carpathian basins. [ABSTRACT FROM AUTHOR]