Podłoże permu w okolicy Szydłowca

Halina Żakowa, Krzysztof Radlicz, Jan Malec


 Omówiono wyniki rewizji podziału utworów dewonu z otworu wiertniczego Ostałów l, występujących pod permem górnym na głęb. 1497,5-2133,0 m. Na podstawie nowych badan mikro- i makrofauny wydzielono utwory emsu, eiflu (w tym dolnego) i żywetu, o łącznej miąższości rzeczywistej ok. 480 m. Wyróżniono 5 grup mikrofacjalnych i określono środowiska sedymentacji. Utwory dewonu porównano pod względem litologicznym i faunistycznym z profilem dewonu synkliny bodzentyńskiej z podkreśleniem podobieństw w wykształceniu dolnego eiflu Ostałowa i niższej części formacji grzegorzowickiej.




Geological structure of the above mentioned area was hitherto interpreted with reference to general premises on regional development of strata, some geophysical surveys, and scarce, unpublished data on the Devonian in the only deep borehole so far made - Ostałów 1. The borehole, localised about

10 km NWN of Szydłowiec (Fig. 1), was made in the years 1962-1963. On the basis of results of preliminary studies, the encountered strata were assigned to the Upper Devonian and Givetian, with reservation (Fig. 2A). Reanalysis of that section became nowadays necessary for more reliable correlation with those of the Góry Świętokrzyskie Mts and Lublin region and in connection with drillings planned for the next years in the Szydłowiec-Opoczno zone. However, only limited amount of core material from that borehole has been preserved in the Świętokrzyski Branch of the Geological Institute in Kielce. The paper presents results of revision of subdivision of the Devonian in the borehole column Ostałów I (Fig. 2B) and the recorded paleontological material is here figured for the first time (Tables I-V). The studies were carried out using better and more universal methods than previously. Nevertheless, several stratigraphic questions remained open because of scarcity and insufficient preservation of the core material.

In the borehole column Ostałów 1, Devonian strata with real thickness of about 480 m occur beneath Permian (depth interval 1497.5-2133.0 m). Their top has been delineated on the basis of well logs. Down to the depth of 1695.8 m there occur strata of series of clay-dolomitic mudstones with intercalations of wackes and quartz arenites and bentonite claystones, and underlaying dolomitic claystone series, with real thickness of about 160 m. The two series were assigned to the Givetian, mainly on the basis of lithological correlations with Devonian section of the Bodzentyn syncline. The next interval (1695.8-1962.4 m - real thickness of about 200 m) comprises limestones, locally of the Styliolina type, in upper part, and a series of dolomites and dolomitic claystones the lower. Organic material, although sporadical, comprises brachiopods the range of which is limited to the Middle Devonian, and some taxa very close to those known from the Eifelian. The series, generally assigned to the Eifelian, may correspond to dolomites of the Wojciechowice Formation and lower part of the Skała Formation in the Bodzentyn syncline. Strata from depth interval 1962.4-2004.8 m (real thickness of about 35 m) have the best paleontological record as they are represented by bioarenite-rudite limestones and dolomitic claystones very rich in organic remains. The presence of Kozlowskiella corbis (Dahmer) and Arikloedenia magna Adamczak makes possible assignation of the strata to Lower Eifelian and drawing arbitrary lower boundary. The dating is further supported by tabulates; some brachiopods, and a crinoid Cupressocrinites gracilis Goldfuss.

The Lower Eifelian from Ostałów is highly similar in lithology and the faunal record to strata of lower part of the Grzegorzowice Formation from the Bodzentyn syncline. A series of dolomitic claystones from depth interval 2004.8-2133.0 m (real thickness of about 85 m) was assigned to the Emsian mainly taking into account the lack of the above mentioned taxa.

Five microfacies groups have been differentiated: micrites and pelites - M, terallochem micrites and pelites - TAM, immature deposits - IMR, submature deposits - SBMR, mature deposits - MR, supermature deposits - SMR, and textural inversion deposits - TI. The latter include, among others, Lower Eifelian bioarenite-rudite limestones. They represent taluses formed at the foot of biolithite build-ups in zone of evaporation shoals and open sea (Fig. 3). Sedimentological analyses also showed that clay and clay-mudstone sediments represent zone of quiet water. Bentonite intercalations encountered in upper part of the Devonian section reflect volcanic activity, and sandy intercalations – temporary increases of hydrodynamic energy' in generally shallow basin.

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