Uwagi o rozprzestrzenieniu osadów piroklastycznych w ordowiku na Niżu Polskim

Abstract

Wykonano próbę analizy ilościowej rozprzestrzenienia osadów piroklastycznych w ordowiku na Niżu Polskim. Wyciągnięto wnioski dotyczące położenia źródeł tego materiału i kierunków jego transportu. Z przeprowadzonej analizy wynika, że ordowickie osady (piroklastyczne można wiązać z wulkanizmem geosynkliny kaledońskiej Europy Zachodniej i Środkowej. SOME REMARKS ON DISTRIBUTION OF PYROCLASTIC DEPOSITS IN THE ORDOVICIAN OF THE POLISH LOWLANDS Ordovician deposits from the Polish Lowlands are intercalated with thin layers of pyroclastic deposits represented by bentonites or, sometimes, tuffites and concentrations of biotite scales in claystones and marls. The stratigraphic range of these pyroclastic intercalations is fairly wide as they occur from the Lower Arenigian (= Latorpian stage) to Lower Ashgilian (= Pirgu stage). A more detailed analysis showed that they are confined to some stratigraphic links, being separated by more or less thick series practically without pyroclastic deposits. The pyroclastic intercalations are most common in the Lower Caradocian comprising graptolite zones Diplograptus molestus and Climacograptus wilsoni, i.e. the Idavere – Johvi – Keila stages.Maps of summative thickness of pyroclastic deposits (Fig. 3) and of number of pyroclastic layers (Fig. 4) were made for quantitative assessment of distribution of these deposits. The maps give some indications concerning the direction of transport and location of source areas of the pyroc1astic material. There is noted a marked increase in both summative thickness of pyroc1astic deposits and the number of pyroclastic layers towards the west. The stratigraphic range of these deposits also increases in that direction. This may be interpreted as the result of approaching to the sources of that material. Similarly as in the case of Ordovician bentonites from Scandinavia and Baltic Republics of the U.S.S.R., the origin of these pyroc1astic deposits from the Polish Lowlands may be explained byvolcanic activity in Caledonian geosyncline in western and central Europe.