The Duksung fan delta is located on the strike-slip fault-bounded western margin of Pohang Basin (Miocene), SE Korea. The fan delta is approximately 6 km in radius and consists of alluvial fan, Gilbert-type topset, foreset, and bottomset, and basin plain. This paper concerns the Gilbert-type topset, which is characterized by stacked units (lobes) of small-scale nested foreset (less than a few meters in height) and coarsening (to fining)-upward cycles (a few meters in thickness) of conglomerate and sandstone. Each lobe prograded radially away from the sediment source with a radius of about 2 km and formed thick (>150 m) shallow marine successions. We suggest that the relative rise in sea level was largely due to marginal normal faulting during expansion of the basin, instead of eustatic sea-level rise.