VOLUME 21 (1)/February 1991

Foraminiferal populations consisting of Albian sediments in the western and central parts of North Bulgaria are analysed. On the base of the regularities in the vertical distribution of the species, from the bottom upwards, two zones and four subzones are subdivided and defined: (I) Lingulogavelinelia albiensis albiensis Zone with subzones – (a) Lenticulina turgidula – Lingulogavelinella albiensis albiensis Subzone (Lower Albian); (b) Lenticulina pulchella – Arenobulimina macfadyeni Subzone (Middle Albian); (2) Arenobulimina chapmani Zone with subzones – (a) Lingulogavelinella cibicidoides – Tristix excavata Subzone (Upper Albian); (b) Eggerellina mariae – Valvulineria praestans Subzone (Upper Albian).

R. Combémorel, M. Stoyanova-Vergilova. Biostratigraphy of the Lower Cretaceous belemnites in France and Bulgaria. Comparative analysis. In Bulgaria the Lower Cretaceous belemnites become abundant as late as the beginning of the Hauterivian Stage. At the same time, the French belemnite faunas, still rare in the Berriasian, where a few species are to be found coming from the Tithonian, gradually become richer as the Valanginian develops. In the latter they are of a considerable stratigraphic significance. From the Hauterivian through the Aptian Stage the belemnites faunas in both countries grow quite varied, being much richer in Bulgaria. Through the Aptian Stage the belemnites decrease in variety, especially in France. The belemnites fauna diminishes much more gradually in Bulgaria, where a number of species from the European and Tethys provinces persist till the Cenomanian.

During the Upper Cretaceous, the land concerned in this study was part of an extensive area of monotonous tectofacies evolution involving a spatially uniform, rhythmic (mostly flysch), carbonate-terrigenous and volcanic-terrigenous (there was active volcanism in adjacent areas) sedimentation, the general monotony being broken by events of olistostrome deposition and consedimentation block movements restricted both in space and in time. From the north to the south, the post-Illirian structural pattern has been found to involve parts of the Illirian Luda-Kamčija synclinorium and the contemporaneous Kačulka anticline and Vrailec anticlinorium surrounding it from the south. By either thrust faulting or recumbent folding, the latter's western periclinorium was overlaid by the northeastern margin of the eastern end of the Laramide Srednogorie anticlinorium, the margin manifesting intense polyphase deformation and block fragmenting. The existence of the so-called Kozuina syncline, named after a mountain peak west of the town of Sliven, has not been confirmed in this study. Essential structural differences have been found between the Srednogorie anticlinorium and the adjacent major Illirian folds. In the area studied, there is the largest areal concentration of faults of Tvârdica orientation and Upper Cretaceous tectonic activity indicating that the Tvârdica strike-slip fault set axis active during the Upper Cretaceous geochron to the south of the Balkan Range should be sought there.