Stratygrafia osadów triasowych w Byczynie koło Jaworzna

Abstract

STRATIGRAPHY OF THE TRIASSIC DEPOSITS AT BYCZYNA NEAR JAWORZNO (EASTERN PART OF THE UPPER SILESIAN COAL BASIN)

The Triassic section occurring at Byczyna (approximately 45 km west of Cracow) embraces the deposits of the Buntsandstein and the Lowelr Muschelkalk. Going from the bottom we may distinguish here the following lithostratigraphical members (Fig. 1):

1. The beds from Świerklaniec. This is a series of continental deposits represented by sands and arenaceous clays, the total thickness amounting to 12-19 m. Red, unstratified arenaceous clays containing singIe quartz pebles play here most important role. They are interbedded by green clays revealing a distinct stratification, and at the top pass into dolomitic clays.

2. The beds with Myaphoria costata, 31-35 mm in thickness. This is a series of yellowish-grey, mady dolamites that contain intercalations of clays and dolomitic marls, as well as intercalations of detrital, calcareous and oolitic dolomites. In dolomites, the peIecypod fauna, mainly Myophoria costata and Hoernesia socialis, is abundant. The beds under consideration show a binary character that may be seen in a succession of marls and dolomites (two sedimentary cycles). The lower part - series A - embraces a bank of the arenaceous diolomite, the lower intercalation of marls and the bed of calcareous and detrital dolomites. The upper part - series B - begins with marIs (upper intercalation of dolomitic marls) that pass towards the top into marly, detrital and oolitic dolomites.

3. The Lower Gogolin beds embrace three stratigraphical members. The lower member is represented by the limestones with Pecten and Dadocrinus (7-10 m). The limestones are distinctly bedded, crinoidail detrital or pelitic, intercalated by marls. Within the series an intercalation of dolomitic limestone (lower cellular limestone) appears, and at the top a characteristic bank of crinoid limestone occurs. Higher up, there rests wavy limestone I (4-4;5 m in thickness). This belongs to the pelitic and marly limestones, characterized by wavy stratification, or the nodular limestones with marly intercalations. In the top postion of the beds considered a bank of cellular limestone appears, 1,5-2,3 m in thickness. This is a calcareous dolomite probably formed as a result of secondary metasomatic alterations.

4. The upper Gogolin beds may be subdivided into three parts. Immediately on the cellular limestones there rests a congolomarate series (9-12 m.) developed as thin- and middle-bedded pelitic and organodetritic limestones with numerous marl intercalations. 2-3 banks of calcareous intraformational conglomerates are here a characteristic element. The second member is represented by the wavy limestone II, revealing small thickness (1,7-2,2 m.), but distinctly expressed wavy and nodular textures. This series is overlain by marly limestones, from 3 to 8 m. in thickness. These are thin-bedded limestones intercalated by marls.

5. Ore-bearing dolomites reach 46 m. in thickness. These make a monotonous series developed as yellow, brown, compact, fine-crystalline or middle-crystalline dolomites. Near the base they sometimes contain small accumulations of pyrite and galena, as well as some concentrations of earthy galmeis. In the upper parts of the section, the dolomites containing siliceous (Fig. 1).

Chemical analysis of the Triassic limestones, marls and dolomites from Byczyna show (Fig. 2). That in the individual stratigraphical horizons are found formations of different composition; the beds from Świerklaniec are of Upper Buntsandstein age (partly probably of Middle Buntsanstein age). The beds with Myophoria costat a have been referred to the Roethian, the Gogolin beds and the ore-bearing dolomites have been assigned to the Lower Muschelkalk. The ore-bearing dolomites have been reckoned to be a formation originated before the epigenetic dolomitization of the limestone rocks (S. Siedlecki, 1948, 1952). At Byczyna they replace the , uppermost part of the Gogolin beds (wavy limestone III) and the lower part of the Olkusz beds (Gorazdeckie beds). The boundary between the, metasomaticaIy changed Gogolin and Olkusz beds may be distinguished within the ore-bearing dolomites on the basis of the existing flints that are frequently found in the Olkusz (Gorazdeckie) beds (Fig. 1). The lower boundary of the ore-bearing dolomites runs, within the area studied, in marly limestones; however, within the areas remote about 5-10 km to the east and west (Trzebionka and Szczakowa) it declines as far as the Roethian so that the ore-bearing doomites replace the whole Gogolin beds, and the secondary metasomatic alterations may, at places, be observed even within the dolomites of the beds with Myophoria costata.