Nove poznatky o vyvoji svrchniho cenomanu v Lobci u Kralup nad Vltavou

In Kralupy nad Vltavou and its surroundings, the Upper Cenomanian Peruc-Korycany Formation of the Bohemian Cretaceous Basin represents an important and well-accessible geological phenomenon to such a degree that the profile in Hostibejk was chosen as a stratotype of the Korycany Member. We report here about a new locality situated northward of the famous inactive quarries at Lobeč, between the towns of Kralupy nad Vltavou and Nelahozeves (Fig. 1). The locality was found by chance by the first author in 2006 during temporary building excavations (Fig. 3), so it is, unfortunately, inaccessible today. All Upper Cenomanian Units sensu Svoboda’s local lithological subdivision, which are typical of that area (Fig. 2), were identified there too, i.e., the so-called Units A, B, C and base of E. However, an unusual bed of gravel between Units C and E was documented (Fig. 4). The dominating massive gravel shows a specific lithological character (matrix is fine-grained clayey sand or sandy clay, pebbles are either rounded quartz clasts originating from Carboniferous arkoses, or lydite, spilite, and Proterozoic shales), which is not seen at the two neighbouring localities of Hostibejk in the S (Figs 1 and 2, locality/profile 3) and Nelahozeves in the N (Figs 1 and 2, locality/profile 5), with only rare pebbles. This discrepancy points to some sheet wash from the SE in the form of a very narrow marine current. The source of clastic material for the newly described gravel was probably located southeast of Kralupy nad Vltavou, where the Upper Carboniferous arkoses found in the gravel as pebbles occur. Its sedimentation took probably place only after the sedimentation of the Unit C, as we have no record of coarser sediment in this unit.