Staroczwartorzędowe rowy tektoniczne i ich osady

Abstract

OLD-QUATERNARY GRABENS AND THEIR DEPOSITSSummaryFormation of grabens was one of the tectonic processes characteristic of the Quaternary period. The article deals with the grabens found to occur within the marginal pad of the Łódź trough at Wola Grzymalina and Krzepocin (Fig. 1). The Quaternary graben at Wola Grzymalina is situated in the southern part of the Łódź trough, where the Mesozoic basement is strongly dislocated as a result of Laramie activity, after the uppermost Cretaceous time. Within this area a W-E graben of Kleszczów may be observed, filled in with the Miocene, maybe also Eocene deposits. The Miocene deposits, along with the beds of brown coals, are also cut by faults that die out below the clay deposits referred to the uppermost Miocene or Pliocene. The Old-Quaternary graben proves a rejuvenation of tectonic processes here. The axis of the graben at Wola Grzymalina runs almost parallel to the older tectonic elements. In the western area the axis deviates slightly in a north-westerly direction, as compared with the main W-E direction. The width of the graben amounts to 0.5-1.0 km, its length being approximately 40 km (Fig. 2). The graben is filled in with arenaceous deposits showing an admixture of rock debris and pebbles of local Jurassic and Cretaceous rocks. Sporadically there appear slides of Tertiary deposits. Some sections disclose a cyclic nature in the sedimentation of sandy deposits too (Fig. 5). The series of these deposits is of fluvial character and has been called the Grzymalina series. Its thickness amounts to 100-150 m, maximum 257 m. This is a thickness unparalleled with that of any series of Quaternary deposits within the southern part of the Lowland area. Within the graben, the thickness of the Quaternary deposits amounts to 318 m at Piaski. The graben at Krzepocin is situated within the north-western marginal area of the Łódź trough, at the boundary of the Kujawy swell (Fig. 1). The Kujawy swell is in this region restricted by the dome-anticlinal structure that runs through Kłodawa and Łęczyca. South-west of the structure the thickness of the Mesozoic deposits in the individual horizons increases (Fig. 4). Here the Quaternary graben of Krzepocin is situated, showing an enormous thickness up to 315 m. The greatest thicknesses of the Quaternary deposits so far known from the vicinity of Łęczyca and Kłodawa amount 150 m (Fig. 6). The graben of Krzepocin is filled in with a series of arenaceous deposits with pebbles and debris of local rocks. These are deposits analogous to the Grzymalina series, but characterized by a lesser thickness (60-85 m). Higher up, in the Krzepocin graben, there rests a complex of boulder clays of the south Polish Glaciation (Cracow Glaciation) showing an unexpected thickness of 96-172 m and a characteristic banded sedimentation. Both composition and character of the deposits of the Grzymalina and the Krzepocin series point to the fluvial origin. The sedimentation bears traces of karst residua. This, and the fact that the deposits occur beneath the boulder clays of the South Polish Glaciation prove that they may be related to the Cromer Interglacial. Consequently, the origin of the grabens at Wola Grzymalina and Krzepocin may be referred to the beginning or to a somewhat later period of the Cramer Interglacial. The throws of the faults that make the edges of the graben are thought to be 100-200 m. However, the tectonic phenomena did not terminate by this single effect. Smaller, local throws, amounting to about fifty metres, were produced during the Masovian Interglacial (Great Interglacial) too, as proved, for example, by a fault that cuts several horizons of boulder clays of the South Polish Glaciation (Fig. 3). An additional lowering of the individual fragments of the graben was possible also during the transgression of the Middle Polish Glaciation, as evidenced by a distinct increase in thickness of the ice-dammed lake deposits of this age. The graben at Wola Grzymalina may be thought to be a classical phenomenon of the deep rejuvenated tectonic processes. The formation of the graben at Krzepocin was conditioned also by a displacement of salt masses from the marginal parts of the dome towards the still living Kłodawa salt dome. The deposits of the Grzymalina series and of the Krzepocin series should be regarded as type examples of facies of the Old-Quaternary grabens in the southern area of the Polish Lowland.