Preservation and Completeness of Fluvial Meandering Deposits Influenced by Channel Motions and Overbank Sedimentation

Assessing the contribution of geomorphic processes to the (non-)preservation of sedimentary deposits is necessary to account for potential bias in measured accumulation rates in the stratigraphic record. In this study, a series of numerical simulations of fluvial meandering successions is performed using FLUMY, a model of channel motions and sedimentary facies deposition. We develop tools to measure non-deposition (stasis S) and reworking (R) of previously deposited sediment between iterations, which are both generators of hiatuses in the sedimentary record. We then compare S and R with measurements of accumulation rates and completeness (C). Results show that combining measurements of both topographic and facies changes allows for a better record of surface evolution than measuring topographies only. Accumulation rate dependence on measurement time span allows distinguishing between two regimes. The first one (anti-persistent) is characteristic of channel avulsion and compensational stacking until the whole domain is visited by overbank deposition, corresponding to the visitation timescale T-v. In the second regime (persistent), reworking by channel migration is the remaining active process until the whole system has aggraded one channel depth, corresponding to the compensation timescale T-c. Based on these results, we propose a new simple formulation based on stasis and reworking to estimate average completeness.