Budowa geologiczna rejonu bełchatowskiego

Abstract

GEOLOGICAL STRUCTURE OF THE BEŁCHATÓW REGION Summary The paper presents a summary of reports prepared by the authors and published in the Guidebook of the LII Meeting of the Polish Geological Society in the Bełhatów area. INTRODUCTION The first survey of deep structure of the Bełchatów area has been carried out with the use of gravimetry methods by the Seismos enterprise in years 1940-1944. Some years later, the regional mapping by the same method has been carried out by S. Pawłowski (1951) and W. Duda (1953). Subsequent geophysical surveys and numerous drillings (J. Grzywacz, Z. Wiśniewski, A. Kozera, K. Kroczek, 1959-1962) showed that the recorded negative anomalies are related to density contrast of Jurassic and Cretaceous rocks on the one hand and the Tertiary on the other hand. At the contact of these rocks, there exist a fault zone and accompanying trough, infilled with Tertiary rocks in Mesozoic basement. The recorded mass deficit is mainly related to presence of brown coal seams. STRATIGRAPHY The oldest rocks found in the Bełchatów area are these forming salt dome and its anhydrite-gypsum cap rock (Z. Dąbrowska, 1965). Seismic surveys and drillings, made at the suggestion of E. Ciuk and Z. Werner (1972), showed that the dome is about 775 m long and 550 m. The dome pierced Upper Jurassic, Cretaceous and Tertiary rocks and it is overlain by the Quaternary, 47.3 m thick. It is built of rock salt with NaCl content ranging from 96.5 to 99.4%), the oldest layer of which belongs to the •tage Z1 (Werra) (according to J. Poborski and Z. Werrner, Fig. 2). The Lower Jurassic (Toarcian) was encountered by a few drillings in the core of the Łękińsko anticline (J. Kopik and T. Marcinkiewicz). It is represented by sandy clay-siltstone rocks with clay and clay-sandy shales with Estheria sp. sp. in the top. The Middle Jurassic is mainly represented by Upper Bajocian (Kuiavian), Bathonian and Callovian rocks enveloping the core of the Łękińsko anticline. The Upper Jurassic is well known thanks to detailed analyses of over 260 borehole columns (Z. Dąbrowska, L. Malinowska, L. Karczewsiki, W. Bielecka). Upper Jurassic rocks of the Bełchatów area do not differ from those of the Łódź Basin, typical of that series, in lithological composition. The Oxfordian is here represented by gray marly siltstones and, in upper part, limestones with flints, and marly layers. Marly limestones and marls of the Kimmeridgian yield rich microfauna and numerous ammonites (Ataxioceras, Rasenia and others) as well as brachiopods, gastropods and bivalves. The Cretaceous occurs at margins of the Łękińsko and Dąbrowa Rusiecka anticlines, built of the Jurassic. It is represented by clastic Albian and carbonate Upper Cretaceous rocks. The major role in development of lithostratigraphic sections of the Tertiary was played by formation of subsiding structure (Bełhatów = Kleszczów Trough), in which thick Upper Tertiary series originated (E. Ciuk, M. Piwocki). In the Kleszczów Trough, the Paleogene is represented by decalcified, silificated and loamy regolith formed on Mesozoic bedrock and usually 2-4 m tchick. Tertiary section of the Trough mainly comprises Neogene rocks, the thickness of which usually ranges from 120 to 250 m. The rocks were assigned to the Miocene and, partly Pliocene (I. Grabowska, L. Jakubowska, J . Mamczar, M. Ziębińska-Tworzydło and E. Woźny - Figs. 3-5). In the Quaternary section, the following stratigraphic units were recognized: Preglacial, Cromerian Interglacial, South-Polish (Cracow) Glaciation, Masovian Interglacial, Mid-Polish Glaciation, Eemian Interglacial, Baltic (Vistulian) - North-Polish Glaciation, and Holocene (M. D. Baraniecka, Z. Janczyk-Kopikowa, A. Makowska, J. Rzechowski, Z. Sarnacka, S. Skompski - Figs. 6-8).