This study presents the first detailed biostratigraphic analysis of calcareous nannofossils and Alveolina assemblages from the Mojen section in the Alborz Zone, North Iran. By integrating Alveolina distribution with nannofossil biozones, the research shows that the NP10 (CNE3) to NP12 (CNE4) zones correspond to the Shallow Benthic Zones SBZ8-SBZ10, representing an early Ypresian age (upper middle Ilerdian to early Cuisian). Furthermore, Alveolina citrea (Drobne) has a longer biostratigraphic range in Turkey and Iran, extending into younger strata within the SBZ7-SBZ9 interval and aligning with the NP zones, highlighting its widespread occurrence across the western-central Neo-Tethys.