Abstract Variations in microfaunal abundance are a useful tool in recognizing basin evolutionary stages. The Western Black Sea basin, situated near a continental passive margin, has three evolutionary phases: flysch, filling, and shelf sedimentation. Flysch sediments accumulated after basin rifting and contain rare and sporadic microfossils. During the filling phase, mostly turbidite sediments accumulated. Their microfossil record shows mixed, rather poor assemblages in periods with increased terrigenous input, but the assemblages are rich in hemipelagic sediments at the tops of turbidite sequences. The most diverse and abundant assemblages occur in sediments of the shelf sedimentation phase. During a basin evolutionary stage, microfaunal abundance shows a gradual upward increase, reaching highest values at the top. A tentative correlation with the supercycles of the Haq et al. (1988) chart is made. This correlation shows that a microfaunal abundance peak is situated in the lower proximity of a supercycle top in the Haq et al. (1988) chart.

Abstract Three planktonic biofacies successions are recognized in the Upper Jurassic and Cretaceous in the Western Black Sea, offshore Romania. Biofacies A (Oxfordian-Valanginian) contains rare Globuligerina tests in punctual occurrences. The planktonic foraminifera are recorded in carbonate inner-shelf deposits in the Upper Jurassic, and mixed (detrital, clayey, marly) shelf deposits in the Berriasian-Valanginian. The first records of the Western Black Sea opening are dated as Valanginian. Biofacies B largely corresponds to the turbiditic interval of the late Albian–Cenomanian. The planktonic foraminiferal assemblages consist of both primitive (globular chambered) and morphologically advanced taxa (keeled Rotalipora and Praeglobotruncana ). The planktonic record is discontinuous, but some claystone levels accumulated under calmer water environments (very low terrigenous input) show remarkable consistency. Biofacies C is peculiar to the outer-shelf deposits of Cenomanian through Maastrichtian age. A gradual increase of the recorded taxa and group diversity is evident. Planktonics are ubiquitous.