Przekrój geologiczny luku Uhruska

Abstract

Na podstawie analizy 10 pełnordzeniowych profili wiertniczych skonstruowano przekrój długości 14 km, tnący skośnie do osi południowe ramię luku Uhruska. Stwierdzono odmienność budowy części południowo-zachodniej, która jest wynikiem działania procesów tektonicznych. W części SE osady kredowe tworzą wyniesienie - zrąb uhruski - przykryte grubą pokrywą utworów czwartorzędowych (do 20 m), głównie gliną zwałową, z porwakami iłów mioplioceńskich. W części NW występuje obniżenie – rów Petryłowa - wypełnione osadami mioceńskiej formacji węgla brunatnego i nadbudowane czwartorzędowymi mułkami, piaskami oraz gliną zwałową i allochtonicznymi osadami ilastymi miopliocenu.

GEOLOGICAL CROSS-SECTION THROUGH THE UHRUSK ARC

The Uhrusk arc is an asymmetric moraine highland rising 200-235 m a.s.l. and parabolically bent to the south-west. The studies on ten fully cored boreholes made it possible to compile a 14 km long cross-section cutting southern arm of this specific geomorphological element obliquely to its axis (Fig. 1). In south-east part of the Uhrusk are, Maastrichtian chalk forms an elevation - the Uhrusk horst, and in the north-western the Petryłow tectonic trough is situated. The trough is infilled with autochtoneous Miocene sands and brown coals (Fig. 2, section IX) and contacting laterally and in the vertical, also autochtoneous Quaternary loess-like muds. The trough-infilling Miocene and Quaternary sediments are overlain (similarly as those of the Cretaceous horst) by glacial sediments with erratic bodies of Miopliocene clays and boulders of Cretaceous rocks and loess-like muds (Fig. 3).

The studies made it possible to differentiate the following stages in evolution of the Uhrusk arc: tectonic remodelling of the basement; origin of the trough and horst (representing tectionic units of the lower order) in result of rejuvenation of the Święcica fault in the zone of the Carboniferous Włodawa Depression (Fig. 4) during the Alpine movements;

- infilling of the Pertyłów trough with sandy sediments, muds, brown coal, and gyttja in the Miocene;

- exaration of a part of Miocene sediments by ice sheet during the South-Polish Glaciation or erosion by glacial waters during the Massovian Interglacial, and origin of a water basin;

- deposition of eolian silty sediments (loess-like muds) in the basin in the Masovian Interglacial; and covering of both sedimentary infill of the tectonic trough and Cretaceous horst by glacial sediments in the Mid-Polish Glaciation times. The sediments and embedded erratic bodies display strong glacitectonic deformations. According to the Authors, Miopliocene clays did not occur in the Pertyłów trough but were brought from fairly large distance. The greatest accumulation of these clays was found at north-western side of the Cretaceous horst.

The surface of the moraine highland, i.e. the Uhrusk arc, was finally shaped in the Holocene.