Dolny tremadok w rejonie Lidzbarku Warmińskiego

Zdzisław Modliński, Bronisław Szymański

Abstract


THE LOWER TREMADOCIAN IN THE REGION OF LIDZBARK WARMIŃSKI

Summary

The eastern part of the Peri-Baltic syneclise has, in the recent years, been an area of intense drilling activity. In 1970, three bore holes (Zaręby 2, Piaseczno 1, and Dębowiec Warmiński 2), situated near Lidzbark Warmiński entered here the lowermost Ordovician formations, i.e. the Tramadocian ones, evidenced palynologically (Fig. 1).
The rock complex of the Lower Tremadocian (Pakerort) in the Peri-Baltic syneclise transgressively rests on the underlying sandstone-siltstone deposits of Cambrian age, being covered with the transgressive glauconite of the Lower Arenigian (Latorp.). Between the Cambrian basement and the complex of the Lower Tremadocian (Pakerort), which occurs at the bottom as a thin layer of basal conglomerate, there exists probably a considerable, though paleontologically not determined in detail, stratigraphical gap. A similar stratigraphical gap is found to occur between the Lower Tremadocian deposits and the higher resting glauconitite of the Lower Arenigain (Latorp). The gap is expressed by a lack of probably younger horizons of the Lower Tremadocian (Pakerort) and of the Upper Tremadocian (Ceratopyge).
The rock complex of the Lower Tremadocian (Pakerort) consists of conglomerates, as well as of medium-grained and variously grained quartz sandstones, intercalated with thin layers and laminae of dark brown, oil clay shales, which are the lithological equivalents of the so-called Dictyonema shales (Fig. 2).
The conglomerate-sandstone rocks contain rich but usually poorly preserved and crushed tests of brachiopods, like Obolus cf. apollinis E d c h w a l d  and Obolus sp. The thickness of the Lower Tremadocian (Pakerort)  deposits amounts, in the Polish part of the Peri-Baltic syneclise, to 2,00–2,3 m.
The Lower Tremadocian formations from the Lidzbark Warmiński region may be correlated with the deposits of the same age from the adjacent areas: Lithuania – the so-called "Obolus Beds" (W. A. Korkutis 1963, 1965); Estonia – Pakerort (A. Loog, E. Kivimägi 1968), and the Podlasie depression in Poland – Obolus sandstones (J. Znosko, 1964; J. Znosko, B. Szymański, 1968; B. Szymański, 1971).
The palaeogeographical and lithofacial studies of the Lower Tremadocian (Pakerort) deposits of the Baltic area allow us to suppose that their fragmentary section, discovered in the Peri-Baltic syneclise, is part of a previously more completely  developed and more regionally extended series which, due to the local palaeostructural predisposition, may have, partly at least, been preserved from the destructing activity of the pre-Arenigian erosion.
The petrographical analysis of the fragmental material of the Lower Tremadocian conglomerates demonstrates that regions deprived of magmatic and !Delta; metamorphic rock exposures were their alimentation are here. In consequence of this, an opinion may be now accepted that the elevated tectonic-morphological element of the platform, i.e. the Mazury-Suwałki elevation, did not constitute in palaeotectonic sense, any uplifted zone or, at least, no crystalline rocks of the Precambrian basement, covered with the Cambrian or Wendian-Cambrian mantle, were exposed or eroded within this area.


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