Efektywna metoda wykrywania przejawów młodej tektoniki w profilach podłużnych rzek Karpat polskich

Witold Zuchiewicz




The Polish segment of the Northern Carpathians is dissected by a number of rivers that run nearly perpendicularly across geological structures of this region (Figs 1, 2). The area in question includes several elevations and depressions which have been active throughout Late Pliocene-Quaternary times, resulting in deformation of planation surfaces (Early and Late Pliocene, Earliest Quaternary), as well as in upwarping/downwarping and/or faulting of rock socles of at least 8 Quaternary strath and erosional-accumulational terraces. The aim of this paper is to stress out the importance of some statistical techniques that would help in neotectonic zonation, as far as river gradients are concerned. The rivers analyzed differ in length (80 to >400 km), relief (430 to >1500 m), and slope (1.8 to >7.5 m/km); they also show variable pattern of the dimensionless semi-logarithmic longitudinal profiles, being subdivided into 4-6 stretches that denote equilibrium/disequilibrium tendencies (Fig. 3). These stretches refer to segments displaying different types of bedrock and, in some cases, young tectonic (active faulting) mobility. A more detailed picture is given by time-sequence plots of river-bed gradients that have been measured on 1 : 25 000 topographic maps for l-km-Iong segments of river profiles (Figs 4-7). Each time the highest possible polynomial order, controlled by the least square method, has been applied. The curves obtained enable one to distinguish river-bed stretches that show anomalously high gradients, as compared to those of the surrounding upstream and downstream reaches. In the West Carpathians (Figs. 8,9), these zones tend to be associated with areas of increased resistance of the underlying bedrock and/or neotectonic elevations (marked by antecedent water-gaps); in middle part of the area studied they delimit some of the most neotectonically (Late Pliocene-Quaternary) elevated zones; whereas in the East Carpathians the high-gradient zones appear to follow the axes oflongitudinal neotectonic elevations (southern part of the Beskid Niski Mts., southern escarpment of the Jasło-Sanok Depression, Strzyżów Beskid Mts), clearly visible on geomorphic and morphotectonic maps. These young elevated areas have been uplifted throughout Quaternary times by some 30-50 m (southern Beskid Niski Mts.) to 150-170 m (Beskid Sądecki Mts.), at rates ranging from 0.05 to ca. 2 mm/yr.