Profile kredy środkowej w północnej części niecki miechowskiej

Abstract

PROFILES OF MIDDLE CRETACEOUS IN THE NORTHERN PART OF THE MIECHÓW TROUGHSummaryThis work is an attempt at separating the Albian deposits from the Cenomanian ones in 12 boreholes made by the Geological Institute (Książ Wielki, Potok Mały, Jędrzejów, Węgrzynów, Jaronowice, Węgleszyn, Biała Wielka, Secemin, Włoszczowa, Milianów, Pągów and Boża Wola) situated in the northern part of the Miechów trough (Fig. 1). In the face of a lack of fauna representatives in these boreholes, the Albian-Cenomanian boundary has been drawn on lithological criteria, by comparing the deposits from the boreholes with the relatively well stratigraphically evidenced Albian and Cenomanian formations already worked out in the outcrop areas, within both limbs of the Miechów trough (S. Cieśliński, 1965, 1970; E. Senkowicz, 1959; R. Chlebowski, 1962; M. Hakenberg, 1969; Z. Sujkowski, 1928, 1934; S. Z. Różycki, 1937, 1938; W. C. Kowalski, 1948; R. Marcionowski, 1970, and a paper in print). The following lithological features, differentiating the Albian deposits from the Cenomanian ones in the north-eastern margin of the Miechów trough, are here the criteria mentioned above: - lack of glauconite or its lesser amount in the Albian than in the Cenomanian deposits; - lack of coarse-grained sand and conglomerate material (apart from basal conglomerate) in the Albian profiles in the area from Brzeźono to Gruszczyn; - occurrence of coarse-grained sand and conglomerate material at the bottom of the Cenomanian deposits at the boundary with the Albian deposits. The appropriate differences for the south-western margin are as follows: - calcium carbonate contents of the Cenomanian deposits, as compared with the Albian ones; - increased contents of glauconite in the profiles of the Cenomanian deposits, as compared with the Albian ones (not everywhere); - occurrence of conglomerates at the bottom of the Cenomanian deposits (not everywhere). Using these differences the authors selected the most probable variants of the position of the Albian-Cenomanian boundary in the individual boreholes (Figs 2, 3, 4 and 5).