Nowe stanowisko z epikontynentalnymi utworami kredy dolnej w rejonie Dębicy

Abstract

W otworze Wola Wielka 2 udokumentowano osady litofacji ilasto-węglanowej górnego walanżynu, zachowane podobnie jak w otworze Stasiówka 1 w formie niewielkiego płata. Bogata fauna aIpejska świadczy o silnym oddziaływaniu środowiska medyterańskiego, co potwierdza tezę, że rejon ten łączył dolnokredowe morze Niżu Polskiego z oceanem Tetydy.

NEW SITE WITH THE EPICONTINENTAL FORMATIONS OF THE LOWER CRETACEOUS IN THE AREA OF DĘBICA

The epicontinental formations of the Lower Cretaceous in the southern part of the Carpathian Foreland were discovered for the first time in 1972 in the borehole Stasiówka 1 near Dębica. In the later period several new boreholes were made in this area. Among them, in the borehole Wola Wielka 2 (Fig. 1) the geological profile containing the formations of Lower Cretaceous was confirmed. In this borehole, under the formations of Miocene (Fig. 2) the formations of Upper and Lower Cretaceous were bored through, ending in the limestones of Upper Jurassic (Kimmeridgian). The sediments of Lower Cretaceous were bored at the depth of 1567.0-1593.0 m. They are developed in two different lithological types of rocks. In the lower part (1581.0-1593.0 m) the bright-coloured pelitic and organogenic limestones (coquinoid limestones) are appearing with the poor fauna indicating Valanginian. In the upper part (1567.0-1581.0 m) the calcareous, mudstones and dark claystones, nearly black with brownish hue, with pelecypods and snails, show the age of Valanginian - Hauterivian. In these formations the rich microfauna was found (Tab. 1, PI. I), which precises more strictly the age of these sediments as Upper Valanginian. It is the alpine fauna, showing that in the region of Dębica the marine basin with the striking reaction of the mediterranean environment existed. Through this area the immediate connection of the Lower Cretaceous sea with the Thetys Ocean was running through. The Valanginian formations of the area of Dębica are generally developed as the sediments of argillaceous-carbonaceous lithofacies. The epicontinental formations of Lower Cretaceous younger than Valanginian were not found in this area, but it is possible to suppose on account of the development of the basin, that at least part of these formations (Hauterivian) was deposited in this area, but that they were later (before Cenomanian) removed by erosion. The strongly eroded surface (Fig. 3) on which, on the Upper Jurassic formations, only a number of small shreds of the formations of Valanginian remained is derived from this period. The sediments of Upper Cretaceous, existing above, provided the sediments of Lower Cretaceous against later removal by erosion. The farther evolution of the Cretaceous basin in the area of Dębica led to the forming of the separate planes of younger sedimentary Cretaceous complexes. The break of deposition and the erosion of Lower Cretaceous and Jurassic formations continued till Cenomanian - Turonian. In this period Upper Cretaceous sea advances from the north and north-west, depositing in narrow, lowered zones, such as palaeovalleys and branches, first the sandstones formations of Cenomanian (Fig. 4) and then, broadening distinctly, the marly-carbonaceous sediments of Turonian - Coniacian. At the end of Coniacian, the sub-Hercynian Phase leading to the regression of the sea belonging to the older ingression of the Upper Cretaceous sea and to district pre-Santonian erosion is marked (Fig. 5). In this region and at the Carpathian Foreland many examples of the transgressive character of Santonian formations, overlying the varied formations belonging to the older ingression of Upper Cretaceous sea (Cenomanian - Coniacian) or even Upper Jurassic are known. The Santonian formations are commencing the sedimentary cover which formed in the younger ingression of Upper Cretaceous sea, lasting till Lower Maestrichtian. The end-effect of the post-Laramide structural and erosional evolution is shown at Figs 6 and 7.