Osady kimerydu i wołgu na antyklinie Lipna

Abstract

Przeprowadzono analizę litofacjalną i stratygraficzną osadów kimerydu i wołgu na antyklinie Lipna. Anomalny profil tych utworów w otworze Lipno 1 spowodowany jest dwoma uskokami, w wyniku których powtórzyły się w profilu osady górnego kimerydu oraz uległy redukcji utwory dolnego i znacznej części środkowego wołgu. Nie wydaje się, aby lokalnie na tej antyklinie miała miejsce przerwa sedymentacyjna w tym ostatnim okresie.KIMMERIDGIAN AND VOLGIAN SEDlMENTS IN AREA OF THE LIPNO ANTICLINE According to J. Dembowska (1979), several lithostratigraphic formations may be differentiated for Kimmeridgian and Volgian sediments known from drillings in the Lipno structure and adjoining areas (Fig. 1). The column of the Kimmeridgian and Volgian from the borehole Sierpc 1 (Fig. 2), fully cored and with rich faunistic material. was accepted by her as a starting point for such analysis. Following J. Dembowska (1979), there were differentiated in that section lithostratigraphic formations: V - Limestone-Marly-Cocquina, VI - Pałuki, and VII - Kcynia. Within the last formation, there were differentiated the Corbula Limestone Member (after J. Kutek et al., 1973) and the Wieniec Member (after J. Dembowska. 1979). Rocks of the Limestone-Marly-Cocquina Formation are known to, yield ammonites of the genera Atuxioceras and Rasenia, indicating their Lower Kimmeridgian age. Rocks of lower part of the Pałuki Formation are dated at the Upper Kimmeridgian on the basis of the records of Aulacostephanus cf. eudoxus (d'Orbigny). A. sp., Amoebocerat krausei (Salfeld), Virgataxioceras fallax (llovayski et Florenski). In middle part of that formation, there were found ammonites of the genus Subplanites, indicating its Lower Volgian age, and in the uppermost part: Zaraiskites cf. zarajskensis (Michalski), Z. cf. scythicus (Vischniakoff) and Z. sp., indicative of the Middle Volgian. Some sediments of the Corbula Limestone Member may still belong to the Lower Volgian as ammonites indicative of the Virgatites virgatus zone (J. Dembowska. 1973) or the Zaraiskites zarajskensis zone (according to J. Kutek et al., 1973) were found in rocks of that member in other drillings in the Warsaw Basin by J. Dembowska (1973). Lower part of the Wieniec Member does not yield ammonites but only ostracodes. The recorded ostracodes: Scabricullocypris trapezoides Anderson, Cypridea valdenensis praecursor Oertli and Klieana alata Martin, suggest its Upper Volgian age. The Skotniki Member is missing in the borehole column Sierpc 1 but it is present in other columns in the Warsaw Basin. being well developed in the columns Gostynin IG I/la and iuromin 5 (Fig. 3). The correlation of Kimmeridgian nad Volgian sediments from the borehole columns Sierpc 1. Kamionki 1 and Lipno 2 (Fig. 2) made it possible to draw the following stratigraphic conclusions. In the borehole Lipno 1 (Fig. 2). top parts of the Paluki Formation yielded Aulacostephanus cf. pseudomutabilis (de Loriol), A. cf. eudoxus (d'Orbigny) and A. elegans Ziegler, which suggest that the whole formation belongs here to the Upper Kimmeridgian. Such interpretation of the age of that formation was accepted by J. Dembowska (1970, 1973) and J. Kutek et al. (1973) who at the same time assumed a stratigraphic gap corresponding to the Lower and a large part of the Middle Volgian. According to the present author, both the increase in thickness of the Upper Kimmeridgian in the borehole Lipno 1 in comparison with these found in the boreholes Lipno 2 and Sierpc 1, and the lack of the Lower and Middle Volgian are due to tectonic factors. The borehole Lipno 1 presumably penetrated a section disturbed by fault lone (Figs. 4 -5) which resulted in repeated occurrence of Upper Kimmeridgian rocks and removal of the Lower and Middle Volgian. Therefore, we are dealing here with an apparent increase in thickness of the Upper Kimmeridgian and the lack of the Lower and Middle Volgian. According to the present author, sedimentary conditions were similar throughout the Lipno structure in the Late Jurassic, leading to origin of similar sediments from the Oxfordian to the Late Volgian, without any break in sedimentation in the Early-Middle Volgian.