Budowa geologiczna podłoża niecki brzeżnej na granicy odcinka warszawskiego i lubelskiego

Abstract

W pracy scharakteryzowano profil utworów dewonu i karbonu na obszarze pomiędzy Warszawą i Dęblinem. Paleozoiczne podłoże niecki brzeżnej, rozdzielone uskokiem Grójca, należy do dwóch odrębnych regionów. W części północnej utwory westfalu A-B spoczywają na .iłowcach ludlowu tworząc płytę zapadającą monoklinalnie ku zachodowi. W części południowej profil jest bardziej pełny. Iłowce syluru (podlasia) przechodzą w osady dewonu dolnego, na których z luką spoczywają osady dewonu górnego. Profil karbonu rozpoczynają utwory wizenu górnego. Na górny namur przypada luka sedymentacyjna i utwory westfalu leżą przekraczająco. W tej części obszaru osady karbonu wypełniają rów mazowiecko-lubelski. W jego obrębie istnieje centralne podniesienie ciągnące się od okolic Lublina.

GEOLOGICAL STRUCTURE OF THE MARGINAL BASIN BASMENT AT THE BOUNDARY OF ITS WARSAW AND LUBLIN SECTIONS

The Mesozoic Marginal Basin is asymmetric along the whole section. Its north-eastern limb gently rises towards the Platform and the south-western is steeper and more rapidly rises towards the Mid-Polish Swell. Moreover, a Mesozoic anticline is found in south-western limb of the Basin SE of Pilica river. This anticline, situated close to the axis of the Marginal Basin, extends to NW as far as the Grójec fault. The shift of ,the Basin axis, found at the Grójec fault line, and the extent of the Cretaceous and Paleogene indicate that the zones separated by this line differ in structure. The Paleozoic sections of these zones are also different. Westphalian A-B (Upper Carboniferous) rooks occur NW of this line (Grodzisk block - fig. 1). They rest directly on tectonically undisturbed Upper Ludlow claystones. The Carboniferous section begins with sandy deposits of the Dęblin Formation, underlain by Mszczonów conglomerates on the west.

The conglomerates are formed of quartzites and siliceous rooks as well as innumerous rhyolite pebbles. The Dęblin Formation is overlain by clay-siltstone deposits and sandstones reappear in large amounts in the uppermost part of the section. In this zone, the Carboniferous increases in thickness from 350 m in the Nadarzyn IG 1 borehole to about 800 m in the Mszczonów IG 2, being overlain by relatively continuous section of the Permian, Triassic, Jurassic and Cretaceous rooks.

South-east of the Grójec trough, there is found Lublin trough. The trough is delineated ·by the Radom-Kraśnik elevation on SW and Kock horst anticline on NE. The oldest rocks recorded in the trough are represented by claystones of the Podlasie stage (Silurian), passing upwards into the Gedinnian. Erosion was predominating in the Middle Devonian so Frasnian rocks are underlain by Devonian rocks of various age. Upper Devonian (Frasnian and Famennian) rocks are known from eastern part of the through. They are overlain by Carboniferous (Upper Visean - Westphalian) rocks which, in other places, rest directly on the Silurian or Devonian. Traces of intra-Carboniferous (Late Namurian) erosion were found in the Carboniferous section in the area adjoining the Grójec fault. The extent of :the youngest Carboniferous (Wesftphalian D) rocks is limited to a small syncline in the vicinity of Magnuszew (Fig. 1).

Three horizons containing redeposited volcanic material were found in the Carboniferous section: fragments of diabases at the base of the Carboniferous, pyroclastic material in somewhat higher part of the section, and fragments of rhyolitic rooks in the top (Westhalian B-C). Palynological analyses showed presence of redeposited older Carboniferous material in the Westphalian B-D. In the trough the Carboniferous is overlain by the Permian rocks which are missing in the Radom elevation. In 'the latter area, the overstepping of Triassic and Jurassic stages was found.

In the area SE of the Grójec fault, the Mesozoic cover is more reduced than in the Grodzisk block and several stratigraphic gaps were recorded. An extension of the elevation -- swell -- known from central part of the Lublin region, was traced in the Mazowsze-Lublin trough SE of the Grójec fault. The elevation separates two basins adjoining marginal parts of the trough. Marginal faults are accompanied by related twin faults which are partly antithetic in character. Their course is related to the origin of the trough as marginal depression of the East-European Platform in the Late Devonian and Carboniferous. The distribution of sedimentary facies indicates the movements did not cease till the Late Triassic.

The available data show that the structures recorded in the Lublin region do not pass the Grójec fault. The author explains this by strike-slip nature of the fault. Differences in the rate movement in different geological periods indicate that this was the zone along which the Lublin block was being shifted throughout the Mesozoic times.