Foraminifera, ostracod and calcareous nannofossil contents of the Cenomanian-Santonian succession are integrated to enhance and refine biostratigraphic divisions and age determinations in the Abu Sennan oil field, Abu Gharadig basin, North Western Desert, Egypt. Foraminiferal (seven), ostracod (eleven) and calcareous nannofossil (seven) zones were identified and correlated with international and local zonal schemes. The boundary of the Santonian age (within Khoman Formation) is delineated by the first appearance of the foraminifera Dicarinella concavata and D. canaliculata; the ostracod Brachycythere angulata and the calcareous nannofossil Zeugrhabdotus scutula and Lithastrinus septenarius. The Campanian age of Khoman B is not recorded due to the existence of a local unconformity surface. The Coniacian–Santonian boundary (top Abu Roash AMember) is characterized by the first appearance of the foraminifera Discorbis turonicus, D. minutum and D. simplex, the ostracodHermanites juxi,Oertliella? dextrospinata, and Cythereis cretaria and the calcareous nannofossil species Quadrum intermedium. The Turonian-Coniacian boundary (base of Abu Roash A Member) is delineated by the first appearance of the ostracod species Spinoleberis yotvataensis yotvataensis, Antepaijenborchella sp. and Cythereis rawashensis rawashensis and the calcareous nannofossils Quadrum giganteum.The boundary between the Cenomanian and Turonian (at basal part of Abu Roash EMember) ismarked by the first appearance of the foraminifera Guembelitria cenomana, Daxia cenomana and Thomasinella punica, the ostracod species Amphicytherura distincta, Veeniacythereis streblolophata and Cytherella aegyptiensis and the calcareous nannofossils species Corollithion kennedyi, Owenia hillii and Calculites cenomanicus. The recorded missing within ages is mainly due to structural elements except for the Campanian of Khoman B which is related to a local unconformity. Paleoenvironmentally, the lithological characteristics and fossil associations indicate that all members of the Abu Roash Formation and the upper part of the Bahariya Formation range from subtidal to inner shelf, except the basal part of Abu Roash E, Abu Roash F andKhoman Bmemberswere depositedwithin openmarine settings.
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