We present the inoceramid and dinoflagellate cyst record from the topmost Campanian–Maastrichtian strata of three key sections of the Western Fore-Balkan Mountains, northwest Bulgaria. The following inoceramid zones were recognized: “Inoceramus” redbirdensis Zone, Endocostea typica Zone, Trochoceramus radiosus Zone and “Inoceramus” ianjonaensis Zone. The Campanian/Maastrichtian boundary was tentatively drawn slightly below the first occurrence of Endocostea typica. The uppermost inoceramid assemblage was confined to the lower part of the upper Maastrichtian. Dinoflagellate cyst ranges, as well as the first and the last occurrence events of dinocysts, provided valuable markers for the stratigraphic subdivision of the Maastrichtian. The first occurrence of Microdinium carpentierae was documented in proximity to the Campanian/Maastrichtian boundary. The Cerodinium diebelii Zone was recognized with a stratigraphical range from the lower Maastrichtian to the lower upper Maastrichtian. The last occurrence of Alterbidinium acutulum was recorded in the lower Maastrichtian and used as aid for tracing the lower/upper Maastrichtian substage boundary. The marked domination of delicate chorate dinocysts in all sections and the encountered low P/G ratio values are indicative of stable low-energy depositional environment and oligotrophic conditions, with normal marine productivity and nutrient availability in the basin during the Maastrichtian.
A scheme of nine ammonite zones for the Bathonian in Bulgaria is described herein. The stratigraphical distribution of the Bathonian ammonites has been revised through new collecting and re-examination of older collections and fields. It has become evident that the criteria for zonal discrimination applied in NW Europe are relevant for Bulgaria to a limited extent, and we cannot compare directly our successions with those from the NW European areas as done in earlier work. Also, many traits of typically Submediterranean dispersal have been found to take a considerable part of the ammonite associations. Therefore, a composite Submediterranean–NW European zonation seems to be applicable to the Bathonian ammonite successions in Bulgaria. The ammonite zonal scale used in previous Bulgarian accounts has been retained, but several changes have been made to attain a more balanced sequence. This scale can be subject to further confirmation and modification, as not enough biostratigraphically well-constrained specimens have yet become available to characterize the ranges and variability of the zones.
With 11 figures In m em ory o f J u l y S t e f a n o v (1932-1966), one o f the m ost talented Bulgarian palaeontologists, on occasion o f his 80th anniversary V a s i c e k , Z., M o t c h u r o v aD e k o v a , N., I l c h e v a , A. & M e t o d i e v ,
This paper presents biostratigraphic data on the Toarcian and Aalenian ammonites in the clayeycalcareous and marly sediments of the Boukorovtsi Member of the Ozirovo Formation and Etropole Formation in a part of the Western Stara Planina Mts. Harpoceras falciferum, Hildoceras bifrons, Haugia variabilis,Grammoceras thouarsense, Dumortieria levesquei, Dumortieria moorei, Pleydellia aalensis, Ludwigia murchisonae and Graphoceras concavum Zones have been established and described. That zonal scheme has been correlated to the zonations of different authors in the North-West Europe. About 40 species of 18 genera, refereed to the families Phylloceratidae, Dactylioceratidae, Hildoceratidae and Graphoceratidae have been determined and 24 of them have been established or described at first in Bulgaria. The boundary between the Toarcian and Aalenian has been biostratigraphically traced.
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