Vapnite nanofosilie a stratigrafie nejmladsich kridovych sedimentu na uzemi Jicina

The Upper Turonian - actually the uppermost Turonian strata in the Čeřovka Hill (Jičín) have newly been confirmed by the occurrence of calcareous nannofossils identified in two samples of sediments collected at two new random outcrops in 2012-2015. They exposed marls to clayey marlstones of the Xab, Prionocyclus germari ammonite Zone. These rocks are the youngest Cretaceous non-metamorphozed sediments in the Jičín area. Upward in the section they pass into a thick metamorphic complex of porcelanites with extremely rare macrofauna which originated due an intrusion of Miocene bazanite. The occurrence of the following well preserved nannofossil species in sediments underlying the porcelanites indicates an existence of UC 9b and UC 9c nannofossil Zones. The first sample (“Čeřovka 1”) provided calcareous nannofossils, including Zeugrhabdotus biperforatus, Helicolithus turonicus, Marthasterites furcatus, Lithastrinus septenarius, Eiffellithus eximius and Quadrum gartneri. documenting the Upper Turonian (UC 9b nannofossil Zone). The second sample (“Čeřovka 2”) of very similar composition of nannofossils assemblage moreover contains Broinsonia parca expansa, documenting UC 9c nannofossil Zone. Several nannofossil species of paleoecological and environmental significance have also been recorded, including Lucianorhabdus maleformis, L. quadrifidus, Braarudosphaera bigelowii bigelowii, Thoracosphaera operculata and Kamptnerius magnificus. The Coniacian nannofossil marker species (Micula sp.) were not found, and rare occurrence of Marthasterites furcatus is discussed. Therefore, the uppermost Turonian age of the second sample is assumed. In this view, the presence of the Turonian/Coniacian boundary inside the overlying porcelanite complex cannot be excluded.