Utwory ordowiku w synklinie bardziańskiej

Wiesław Bednarczyk, Roman Chlebowski, Zbigniew Kowalczewski




The paper deals with the Ordovician formations encountered in three new bore holes made by the Department of Iron Ore Deposits of the Geological Institute in the area of the southern limb of the Bardo syncline (Fig. 1). In the bore hole Mokradle I (Fig. 2) the Ordovician rests on the sheared formations of the Lower Cambrian (Holmia beds). It begins with the Kozielskie beds (uppermost Upper Tremadocian - according to W. Bednarczyk, 1964) represented by a sandstone-spongiolite-mudstone series, approximately 2,3 m in thickness, among others with Lingulella insons lata Koliha. Higher up, there are found quartzite sandstones with Modestospira polonica (Gür.), about 10 m in thickness, belonging to the Bukówka beds (Lower Arenigian). The Ordovician ends with the Dymińskie beds (Upper Arenigian) developed as (from the bottom) dolomites, claystones and limestones with the following fauna: Orthis callactis Dalm., Rauna wołchowiana Öpik, Acontiodus cf. rectus Lindstr. In dolomites are found bentonite intercalations, and at the bottom of the claystones are accumulations of mudstone material with chamoisite. Thickness of the Dymińskie beds amounts approximately to 6,8 m. On the Ordovician there rest in tectonically discordant position clay shales with intercalations of lydite, representing Llandovery. The remaining two bore holes belong to the shallow reconnaissance ones. Encountered here but not pierced Ordovician deposits are represented by glauconite mudstones with chalcedonite (Kozielskie beds) 1 m in thickness, covered with the Wenlockian claystones (bore hole Ociesęki 1) and the Dymińskie beds developed at the base as marls with Productorthis obtusa (Pand.), as well as arenaceous mudstones with brachiopods (Antligonambonites sp., Productorthis sp., Cyrtonella ? s.) and trilobite (Cybele). Thickness of the formations mentioned above amounts approximately to 8,5 m (bore hole Ociesęki 3, Fig. 3). The research has also demonstrated that marine transgression began at the turn of the Lower and the Upper Tremadocian, and definitively covered at the Lower Llandeilo time the continent formed during the Sandomirian phase. Some local shallowings and emergences took place in several regions within the central part and in the west, however, without any influence upon the character of the basin. The present authors have demonstrated in the part devoted to tectonical conclusions that three distinct structural stages can be distinguished within the Bardo syncline ,i.e. Cambrian, Ordovician-Silurian and Devonian stages. These were formed during the successive mountain-building phases of both Caledonian and Hercynian orogenies.

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