Abstract. Investigations carried out on 22 drillings on the Southern onshore area of the Romanian Black Sea and on one drilling from the Southern offshore area of the Romanian Black Sea are presented here. The lithological/sedimentological investigations and the micropalaeontological (calcareous nannoplankton) quantitative and qualitative analyses revealed several depositional sequences. The oldest identified sedimentary cycle is latest Jurassic Tithonian) - Early Cretaceous (Berriasian - Valanginian) in age and composed of marine shallow water carbonates. The next cycle, in stratigraphic order, is Barremian - Early Aptian in age, composed of marine shallow water carbonates. A fluvial-lacustrine formation, Middle - Late Aptian in age, was observed only in the drillings from onshore area. The youngest Cretaceous cycle (Santonian – Maastrichtian) is mainly composed of chalks, with intercalations of glauconitic sands towards the base. In the chalk offshore deposits of the Black Sea, a continuous sedimentation took place within the Cretaceous/Tertiary boundary interval. The Paleogene deposits (Middle – Late Eocene) are characterized by the presence of marlstones and claystones. These are overlain by Oligocene black shales, rich in organic matter and fish remains. Miocene, Pliocene and Pleistocene deposits were sedimented in a brackish environment, but several marine influxes probably occured (based on the nannofloras encountered) within the Middle Miocene, latest Miocene-earliest Pliocene and Late Pleistocene. The Cretaceous-Eocene nannofloras are dominated by warm water taxa (Tethyan nannofloras). The occurrence of the Cretaceous calcareous nannoplankton confined to high latitudes (Boreal taxa) within the Late Valanginian, the Barremian - Aptian boundary interval and the latest Maastrichtian, indicate cooler water surfaces. A more significant cooling could be assumed in the Early Oligocene, occuring at the same time with the separation of the Paratethys Realm, and with the appearance of endemic nannofloras in the Black Sea offshore area
