Stratygrafia ordowiku w wierceniu Jezioro Okrągłe 1

Zdzisław Modliński, Jędrzej Pokorski




Silurian, Ordovician and Cambrian deposits have been pierced under the arkoses of Lower Permian age in bore hole Jezioro Okrągłe 1 made in the south-eastern area of Poland. Ordovician section begins with the Upper Arenigian deposits that immediately overlie the (Lower?) Cambrian formations. Arenigian (945.2-941.8 m) is represented by red clayey and marly-calcareous deposits at the horizons Megistaspis limbata and Asaphus lepidurus. In Llavirnian (94l.8-921.0 m) are found limestones, grey-green at the bottom and brown-red and variegated in the higher part. The occurrence of ferruginous oolite horizons is a characteristic feature of these deposits. Here, four faunistic horizons have been distinguished, characterized by definite assemblages of trilobite fauna. Llandeillian (921.0-914.0 m) is built up mainly of organo-detrital limestones, grey in colour. However, the faunistic documentation of this stage is very scarce. Caradocian deposits (914.0-881.0 m) show a considerable lithological differentiation. They are represented by marly organo-detrital limestones and by marls, yellow-green in colour. Thin intercalations of bentonites, found to occur in the deposits of idavere horizon, are worthy of being stressed here. Rich trilobite and brachiopod fauna allows to subdivide these deposits into horizons and to correlate them with the Estonian equivalent horizons. In Ashgillian (881.9-851.5 m) are found marls and marly limestones, frequently with nodular and ball textures, as well as limestone breccias. At the top of the Ashgillian deposits, in the horizon Dalmanitina mucronata, a fairly considerable admixture of terrigenous material appears, too. Without any sedimentary break, or wash-out traces, the limestone-marly facies continues in the Lower Llandoverian. The Ordovician deposits encountered in bore holes Gołdap and Jezioro Okrągłe distinctly differ from those found to occur in the region of Kętrzyn and Bartoszyce (Z. Modliński, 1967). The Kętrzyn-Stoniszki elevation was an area that separated these two regions where also a change of facies took place (Fig. 2).


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