The Upper Cretaceous succession (Coniacian to lowermost Maastrichtian, with focus on the Campanian) at Petrich, Central Srednogorie Zone in Bulgaria, is described and calibrated stratigraphically based on nannofossils, dinoflagellate cysts and inoceramids. The following standard nannofossil zones and subzones are identified: UC10–UC11ab (middle to upper Coniacian), UC11c–UC12–UC13 (uppermost Coniacian to Santonian), UC14a (lowermost Campanian), UC14b ^TP–UC15c ^TP (lower Campanian to ‘middle’ Campanian), UC15d ^TP– UC15e ^TP (upper Campanian), UC16a ^TP (of Thibault et al. 2016; upper part of the upper Campanian), and UC16b (Campanian–Maastrichtian boundary). The base of the Campanian is defined by the FO of Broinsonia parca parca (Stradner) Bukry, 1969 and Calculites obscurus (Deflandre) Prins and Sissingh in Sissingh, 1977 (a morphotype with a wide central longitudinal suture). The Areoligera coronata dinoflagellate cyst Zone (upper lower Campanian to upper upper Campanian) is identified, corresponding to the UC14b ^TP–UC16a ^TP nannofossil subzones. The inoceramid assemblage indicates the ‘Inoceramus’ azerbaydjanensis – ‘Inoceramus’ vorhelmensis Zone, correlated within the interval of nannofossil subzones UC15d ^TP–UC15e ^TP. The composition of the dinoflagellate cyst assemblages and palynofacies pattern suggest normal marine, oxic conditions and low nutrient availability within a distal shelf to open marine depositional environment during the Campanian.

Biostratigraphic analysis of calcareous nannofossils from the Pełczyska section in the Miechów Trough (southern Poland) has revealed that the entire section covers the lowermost Maastrichtian. The UC16bTP Tethyan subzone is designated based on the presence of Broinsonia parca constricta Hattner, Wind and Wise, 1980, reworked remains of Uniplanarius trifidus (Stradner) Hattner and Wise in Wind and Wise, 1983 and the simultaneous lack of Eiffellithus eximius (Stover) Perch-Nielsen, 1968. The studied section spans also the interval between the LO of Zeugrhabdotus praesigmoides Burnett, 1997 and the FO of Prediscosphaera mgayae Lees, 2007 (UC16 S3 Boreal subzone). Quantitative analysis of nannofossil assemblages has shown the dominance of cold water species (up to 50%), e.g., Micula decussata Vekshina, 1959, Prediscosphaera spp., Arkhangelskiella spp., Calculites obscurus (Deflandre) Prins and Sissingh in Sissingh, 1977 and Lucianorhabdus cayeuxii Deflandre, 1959. In the early Maastrichtian, the studied area was more influenced by cool water masses from the Boreal Province rather than by warm water from the Tethyan Province. The significant predominance of cold water taxa and the elevated presence of Prediscosphaera cretacea (Arkhangelsky) Gartner, 1968 also supports the hypothesis of climate cooling in the early Maastrichtian.

The present contribution provides a study of calcareous nannofossils and siliceous microfossils from the Sawai Bay Formation on Car Nicobar Island, northern Indian Ocean. Two stratigraphically short sediment intervals near Sawai Bay have been examined. Qualitative and quantitative microfossil analyses show the Sawai Bay ‘A’ Section to be devoid of siliceous microfossils, while 24 well-preserved calcareous nannofossil taxa are identified. The Sawai Bay ‘B’ Section yields 18 calcareous nannofossil, 33 radiolarian and 25 diatom taxa. The calcareous nannofossil index taxa ( Ceratolithus armatus Müller, 1974a and C. cristatus Kamptner, 1950) indicate both sections to be from zones NN12 (CN10b) and NN13 (CN10c) of early Pliocene (Zanclean) age. The radiolarian taxa, i.e., Didymocyrtis avita Riedel, 1953, Euchitonia spp., Siphocampe lineata (Ehrenberg) Nigrini, 1977, Stichocorys peregrina Riedel, 1953, Semantis spp. and Stylochlamydium sp. are common in the Sawai Bay ‘B’ Section, which is assigned to Zone RN9. Most of the diatom taxa are represented by representatives of the genera Actinocyclus Ehrenberg, 1837, Azpeitia Peragallo in Tèmpere and Peragallo, 1912, Coscinodiscus Ehrenberg, 1839a, Grammatophora Ehrenberg, 1841 and Triceratium Ehrenberg, 1839b, with the benthic diatom species Triceratium favus Ehrenberg, 1839b being predominant (~35% of the total diatom count). Siliceous microfossils are also represented by silicoflagellates dominated by Dictyocha spp. and sponge spicules dominated by astrophorids.