Cyclic water-sediment supply coarsens the temporal resolution of fluvio-deltaic strata

Fluvio-deltaic deposits archive environmental change, but internal depositional dynamics can modify or erase signals before preservation. Whether a signal survives the stratigraphic filter depends in part on its duration: signals with periods shorter than the time required for a system to smooth its own uneven topography tend to be lost, whereas longer-period signals are more readily preserved. This smoothing timescale, or compensation timescale ( T c ), is well constrained under steady conditions, but how it responds to external forcing remains unclear. Here we combine physical and numerical experiments spanning a range of forcing amplitudes and periods in input sediment-to-water discharge ratio, using a sediment mass-extraction framework to define dynamically equivalent measurement positions across experiments. We show that cyclic forcing increases T c by as much as fourfold relative to unforced controls. Under fast forcing, intermediate amplitudes produce the longest T c , whereas weak and strong forcing amplitudes yield values within 30% of the control. Under slow forcing, T c increases more monotonically with amplitude, reaching two- to threefold above control at the highest amplitudes tested. Basin-scale topographic roughness, rather than local channel depth, is the strongest predictor of T c across both forcing regimes ( r = 0.81–0.89, p < 0.001). These results show that forcing itself modifies the temporal resolution of the stratigraphic archive, so the stratigraphic record is not a passive filter with a fixed cutoff; instead, its temporal resolution coevolves with the amplitude and period of the forcing it records.