O czwartorzędowym ciosie i uskoku w Kotlinie Sądeckiej (Zachodnie Karpaty Zewnętrzne)

Abstract

On Quaternary fault and jointing in Nowy Sącz Basin (Outer Western Carpathians, Poland) The data presented here were collected in the margin of the Nowy Sącz Basin (Fig. 1). This basin is situated on the Magura nappe which is the innermost tectonic unit of the Outer Western Carpathians. The bottom and slopes of the basin are covered by Pleistocene river terraces composed of gravels with loess-like loams inlayers. Two sets of subvertical joints occur in the loess-like loams (Fig. 2, Pl. I, Fig. 1). Joints of the first set are subparallel to the down slope direction. Joints of the second set were found only in one outcrop (Fig. 2B). They are parallel to erosional cutting (Pl. I, Fig. 2). Two surfaces, N35W/65E and N40W/70E, were found in an outcrop near the bottom of the Riss terrace (Fig. 3, Pl. I, Fig. 1). The second one is covered by slickenside with steps and striae pitching at 70° to the SE (Pl. II, Fig. 1). The amplitude of this fault diminishes upwards. At the boundary between loams and gravels the fault dies out changing to a set of tensional fractures (Pl. II, Fig. 2). The disposition of the fractures attests to the gravitational character of the fault. The slip along the fault was opposite to that indicated by „smoothness criterion” (Pl. II, Fig. 1). This seems to present an interesting contribution to the discussion on the orientation of slickenside steps (cf. Dżułyński, 1952, Norris and Barron 1969; Jaroszewski 1972). Orientation of subvertical joints is clearly relief-controlled. It appears that joints subparallel to the down slope direction were formed by mass movements as shear and extensional surfaces. To the nontectonic origin of joints attest strongly their chaotic pattern in the discussed area (Fig. 2). The origin of the fault seems to be different. Reconstructed direction of o3 is N66E. This direction of extension could not be caused by older south-eastward mass movements (Fig. 3). It appears that also the recent mass movements directed to the South as inferred from the subvertical jointing may not be responsible for the fault origin. In the case of such connection one should rather expect a fault dipping to the S than to the NE. Moreover the direction of extension reconstructed for the fault is oriented obliquely to the o* inferred from joints (Fig. 2A). Thus it appears that the fault is of a tectonic origin. The young tectonic movements in the Outer Western Carpathians are interpreted since beginning of the century on geomorphological analysis and geological mapping. However, it remained for Henkiel (1974) and Birkenmajer (1976) to furnish mesostructural arguments. It follows from the observations described in this paper that at least in the Nowy Sącz Basin Quaternary deformations are of gravitational origin. Some of these deformations were controlled by relief.