Ordowik platformy wschodnioeuropejskiej na obszarze Polski

Ewa Tomczykowa



In the last years (1957-1962) the Ordovician·deposits of Northeastern Poland were encountered in 9 deep bore holes, as follows: Lębork, Pasłęk, Bartoszyce, Gołdap, Żebrak, Mielnik, Tłuszcz, Kaplonosy, and within the region of Białowieża at Krzyże and Podborowisko. As may be seen of the profiles of these bore holes, the Ordovician deposits are strongly reduced·revealing only small thickness, at: places. The greatest thickness amounting about 1100 m may be observed at Pasłęk, whereas it attains merely 27m at Tłuszcz, near Warsaw, and only 15-20 m in the region of Białowieża. In the borehole Lębork, the Ordovidan deposits have not been pierced. Here, a part of the Pomeranian beds has been encountered, corresponding to the Caradocian and the Ashgilian stages.

It results of the profiles mentioned above that within the area of the East-European platform, the shallow-neritc, calcareous and calcareous-arenaceous deposits with glauconite were·formed at the bottom in this period. As proved by the intercalations of siltstones with graptolites, and by the general increase in thickness (Pasłęk and Lębork), these deposits tend to deepen towards the west. Moreover, it may be assumed that the sedimentation took place in a shallow and unquiet basin, where a new laid down material was immediately washed off and deposited again. In addition, the laterite sediment may have been brought into the basin from the adjacent continent, as proved by the red colour and intercalations of ooliltes connected with the base level of wave activity.

Frequently, the Ordovician sedimentary cycle begins with a thin bed of conglomerate, overlain by not too thick arenaceous-glauconite deposits characteristic of relatively various stratigraphical position (Table 1).

Higher up, there rest limestone-marly deposits of flowage character, with intercalations of agglomeratic, conglomeratic ,or organodetrital limestones, containing accumulaltions of chamosite oolites. At the bottom and top parts of the deposits, there appear agglomeratic and conglomeratic intercalations, certainly connected with the synorogenic Caledonian movements.

It results of the general analysis of facial distribution that the Ordorvician sedimentary basin was a shallow one over the whole area of Poland. Being of epicontinental character, the basin was, however, open for migration of planktonic and benthonic fauna. The lithological character of the deposits discussed and their fauna, particularly that of the East-European platform area, show a great resemblance to the Ordovician deposits of the Russian platform (T. N. Alichova, 1960), above all, however, to those of the Baltic countries (A. Roomusoks, 1960; I. Paskevicius, 1960). Moreover, several profiles, i.e. from Bornholm and from the area of analogous with those of the Ordovician from Bornholm and from the area of Sweden (P. Thorslund, V. Jaanussori, 1960). It should be stressed here that deposits of this age, occurring in the central and southern parts of the Święty Krzyż Mts., also are distinctly silmilar, mainly due to the arenaceous-calcareorus development and the assemblages of trilobites and brachiopods (J. Czarnocki, 1948; H. Tomczyk, 1962).

The Silurian platform deposits have for the first time been subdivided by the present author from the regional point of view, mainly .on faunal assemblages. The author detaches several distinc complexes of strata and introduces a new nomenclature for the units under study.

Basing on the introduced subdivision, the author substantiates here that the Białowieża beds characteristic of the Tremadocian and Arenig formations occur lowermost in the profile. The overlying Pomeranian beds, lower, middle and upper ones, embrace the Llanvirnian, Llandeilan and Caradocian stages. The uppermost Ordovician stage ends with the Mazury beds (H. Tomczyk, 1962), corresponding to the Ashgilian stage.

A more detailed description of the beds and of the stratigraphical complexes discussed above, also a list of faunal assemblages studied, as well as discussion on lithofacial character of the deposits are given in the Polish text.

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