Wykształcenie litofacjalne i konodonty wizeńskiego profilu Z okolic Olkusza

Abstract

Lithofacies and conodonts in Visean profile, Olkusz area, southern Poland

The investigated WB-94 borehole profile (100 % core) is located at the north-eastern margin of the Upper Silesian·Coal Basin, in vicinity of Olkusz (Fig. 1). Predominant in the profile (Fig. 2) are dark marly spiculitic calcilutites with layered or lemses-shaped black cherts, comparable to the Wilson's (1975) standard microfacies 1 (PI. 1, Figs. 1-2;Pl. 2, Fig. 1; Pl. 3, Fig. 2). The autochthonous marly beds are intercalated with grey to pinkish homogeneous intrabiosparenites containing abundant abraded and redoposited skeletons of echinoderms, brachiopods, foraminifers (mostly endotyrids), bryozoans and various calcareous·algae (Pl. 1, Fig. 3;.Pl. 2, Fig. 2;·PI.·3, Fig. 1). This microfacies corresponds to SMP 4 and 5 (Wilson, 1975). Laminated fine calcarenites and calcilutites, with cherts in plaes, form the intermediate litological variety.

The biostratigraphic study of 10 (including positive) conodont samples (see Table 1, and Fig. 2 for location in the profile) is based upon the Lower Carboniferous conodont zonation constructed by Austin (1974) with some modifications by Groessens (1974) and Groessens, Conil & Lees (1976). Stratigraphically important and/or taxonomically interesting formtaxa are illustrated on Plates 4-8 and described in the paleontological part.

The occurrence of Gnathodus sp./aff Paragnatthodus commutatus (Branson & Mehl)/and Mestognathus sp. in the lowermost dated sample (215.3 m) indicates that it is not older than the upper part of the Visean Mestognathus beckmanni Zone. In turn, the sample from depth 187.7 m is not younger than the lowermost part of the Visean Gnathodus bilineatus bilineatus Zone as indicated by the stratigraphic ranges of Gnathodus delicatus Branson & Mehl and Gnathodus sp. indet. (Meischner 1970, Boogaert 1967,Higgins 1974, Matthews & Thomas 1974). The uppermost dated sample (depth 183.1 m) contains stratigraphically mixed conodont assemblage with the admixture of the typical Famenian and Tournaisian forms (Table 1). The admixture is most probably related to the redeposition of some contemporaneously eroded Upper Devonian to Lower Carboniferous conodont-bearing carbonates within the Lower Carboniferous shelf platform (cf. Bojkowski & Bukowy 1966, Jurkiewicz & Żakowa 1972). The·investigated lithofacie beIongs to the anaerobic marginal deeper shelf with intense redeposition from the intra-basinaI or coastal shoals inhabited by abundant benthic assemblages.