In this study, the mollusk fauna and stratigraphy of Neogene units exposed in Lapseki (Çanakkale, NW Türkiye) and its surroundings were investigated. A total of 13 measured stratigraphic sections were studied, from which 12 genera and 21 species of Gastropoda, and 10 genera and 15 species of Bivalvia were identified. Based on the paleoecological characteristics of the fauna, it is inferred that brackish water conditions fed by freshwater sources prevailed during the early Romanian in the study area. In the lithologies overlying these levels, which consist of carbonate sand, carbonate sandstone, and marl, brackish water conditions were observed to have developed in the basin, marked by the appearance of species of the mactrid genus Aktschagylia , characteristic of the Akchagylian of the Caspian Basin. The stratigraphic levels to which the fauna corresponds, as identified from bottom to top in the section, were observed to span the period between the beginning of the Late Pliocene and the beginning of the Early Pleistocene, with Quaternary marine terraces at the highest levels. It is inferred that, across different time intervals, the basin exhibited characteristics similar to those of the Dacian and Euxinian-Caspian basins. Fauna likely reached the study area during the latest Romanian (middle–late Akchagylian age) as a result of a transgressive event from the Caspian Basin to the Euxinian Basin.