The Kazusa Group (up to 3000 m thick) is the infill of the Plio–Pleistocene Kazusa forearc basin in the Boso Peninsula of Japan. The lower part of the group is represented by thick successions of submarine fan deposits associated with deep-sea basin-plain and slope deposits. The submarine fan deposits are characterized by repetitions of sandstone-dominated and siltstone-dominated intervals (cycle thickness as much as 270 m thick). Each pair consists of a sandstone-dominated and a siltstone-dominated interval and is a depositional sequence (ca. 0.2–0.05 m.y. cyclicity). In general, sandstone-dominated intervals consist of channel and overbank deposits and age-equivalent sheet-like sandstone beds interbedded with siltstones in down-fan directions, indicating lowstand systems tract deposits. The uppermost part of sandstone-dominated intervals commonly contain chaotic deposits and fine upward to the lower part of siltstone-dominated intervals. These fining-upward successions are age-equivalent to transgressive shelf and slope deposits in up-slope areas and may have developed in response to reduction in active supply of coarse-grained clastic sediments to a deep-sea environment during transgressive stages. The remainder of siltstone-dominated intervals are characterized by thin- to medium-bedded sandstones and interbedded siltstones. Bed thickness and grain sizes of intercalated sandstones increase up-section and indicate restoration of active supply of coarse-grained terrigenous clastic sediments to a deep-sea environment in response to progradation of shallow marine depositional systems during highstand sea-level stages. The distinctive associations of lowstand, transgressive, and highstand systems tracts in submarine fan successions of the lower Kazusa Group are interpreted to reflect the development of point-sourced, small sand-rich submarine fans in the Kazusa forearc basin. This basin is inferred to be characterized by a narrow shelf, a steep slope, and high sediment supply. Coarse-grained terrigenous clastic sediments in such a setting were supplied to submarine fans during every stage of a relative sea-level cycle. Lithofacies organization of depositional sequences in submarine fan successions of the lower Kazusa Group can represent one type of variation in sequence-stratigraphic models for settings controlled by forearc tectonics that were overprinted by glacioeustasy during the Pliocene through Pleistocene.