Konodonty ordowickie z otworu Kętrzyn

Maria Nehring




The Present works deals with the conodonts found to occur in the Ordovician deposits drilled in bore hole Kętrzyn IG-l (southern Part of the Lithuanian depression). The Ordovician is here developed in a shallow-water facies, its thickness being 68.5 m (Fig. 1). Among the determinable conodonts 30 representative species of 18 genera have been distinguished. In the Arenig, Llanvirn, Llandeilo end Ashgill conodonts are scarcely represented, whereas in the Caradocian they are abundant, proving the age of these deposits determined already by Z.Modliński (1967) on the basis of microfauna. Since among the 26 species, determined in this assemblage 11 have been encountered in the Ordovician deposits only and since the vertical extent of the other 9 species is greater, it seems to be reasonable to regard the conodont assemblage found at the interval from 1557.3 to 1569.0 metres as an assemblage typical of the Caradocian. A detailed analysis of the conodonts from the Ordovician deposits that occur in the vicinity of Kętrzyn allow us to state that the stratigraphical extents of certain species are greater than accepted previously (Table 1). For example, the form Drepanodus deltifer Lind. has so far been known to occur only in the Tremadocian deposits of Sweden whereas at Kętrzyn it is found in the Arenigian deposits. Similarly, Trichonodella alae Lind., determined in the Arenigian deposits of Sweden, has been encountered in bore hole Kętrzyn in the Llanvirnian deposits. As concerns the fairly abundant representatives of the genus Oistodus, which appears in the Ordovician deposits of Kętrzyn, interesting is a fact that Oistodus lanceolatus Pander - a species known from the Lower Ordovician - occurs at Kętrzyn considerably higher. The first specimens that belong to this species are found to occur in Llandeilo, but simultaneously, they are also fairly rich in the beds referred by Z. Modliński (1967) to Caradocian. In summing up, we may draw a conclusion that the assemble of conodonts in study generally proves the stratigraphical subdivision of the Ordovician deposits at Kętrzyn, suggested previously by Z. Modliński on the basis of macrofaunistic and lithological evidences.

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