Lithostratigraphic studies and analyses of the physical characteristics of sediments have provided a detailed picture of the fine-grained deposits in the Suurpelto area in Espoo, southern Finland. A key sediment section from drill-hole N5, which represents different depositional phases of the Baltic Sea Basin (BSB) history, was divided into 11 lithostratigraphic units according to their sediment structure and composition. The properties of these units were carefully described. A 3D geological model of these units in the Suurpelto area has been established, including cross-section profiles from northern and southern parts of the basin. The northern part of the Suurpelto basin contains a thinner sequence of massive and varved clays with coarser (silt, sand) mineral layers representing earlier phases of the BSB than the southern part of the basin. In the southern part of the basin these deposits have been covered by more organic and sulphide-rich sediments that represent later phases of the BSB. Three locations in the Suurpelto area have thicker than average (10.6 m) sequence of fine-grained deposits. The maximum thickness of fine-grained sediment in the Suurpelto area is >25 m in the SW corner.