Sediment flux signals in foreland basins preserve a record of tectonics, sea level and climate through erosion and sedimentation.However, longitudinal sediment transport often occurs in foreland basin,thus removing part of the orogenic material flux from foreland basins.Here we use mass balance calculation and stratigraphic simulations ofsediment fluxes for the Taiwan orogen to provide a quantified order ofmagnitude estimate of how much orogenic material may bypass a forelandbasin. Our results indicate a significant, potentially more than 50%,mismatch between sediment volume currently preserved in the basin and theamount of material eroded from the orogen since the onset of collision inTaiwan. This supports previous paleogeographic work suggesting thatlongitudinal sediment transport in the paleo-Taiwan Strait served as abypass conduit important for the establishment of a steady state orogen.We identify candidate submarine topography in the South China Sea thatmay preserve Taiwan's missing erosional mass.