<p>The contribution of buried branch faults to the evolution of sediment-filled basins remains controversial, particularly in places where deformation is commonly attributed to major boundary faults. Within the seismically active Shanxi Graben System of North China, the Linfen Basin contains thick Cenozoic sediments that obscure its internal structures and our limit understanding of the role of buried faults in its development. The Fendong Buried Fault (FBF), a concealed branch of the Luoyunshan Fault (LYSF) along the western margin of the basin, is inferred to have influenced the basin structure and sedimentation. This study investigated the geometry and activity of FBF using shallow seismic reflection profiles, a borehole-based composite stratigraphic profile, and chronological constraints on Quaternary deposits. Three shallow seismic lines delineate the subsurface trace of the fault, while drilling data confirm its existence and constrain its activity. The results indicate that FBF remained active until the late Middle Pleistocene, with the most recent activity occurring approximately 124–140 ka. The late-stage slip rate was estimated at ~ 0.26 mm/a, with three paleo-earthquake records identified from drilling data. Our analysis suggests that the FBF functioned as an active branch structure that was mechanically linked to the LYSF, exerting considerable control on the eastern boundary of the Linfen–Ganting subsidence center during basin evolution. Its activity weakened following the early Late Pleistocene, likely due to reorientation of the regional stress field and progressive strain localization on the main boundary fault. Overall, our findings provide globally applicable insights into the long-term evolutionary behavior of active basins covered by thick sedimentary successions.</p> Graphical abstract <p></p>