A method to translate between short-term fluvial processes on deltas and bulk volumes of channel and overbank deposits in the stratigraphic record

In the most general sense, the stratigraphy of river-dominated deltas can be classified into channel (sand) and overbank (mud) deposits. The relative proportions of these deposits are determined by the interplay of erosion and deposition between channels and the surrounding floodplain. A simple approach to the problem is to consider that (1) as river channels migrate and avulse across deltas, they remove previous deposits and replace them with channel sand bodies, and (2) overbank flow deposits mud on levees and floodplains. Here we propose a simple relationship between channel mobility and overbank aggradation rate to estimate the bulk proportions of channel sand and overbank mud deposits in the stratigraphic record. We measure the fraction of the delta surface that can be reworked by channels over the time it takes the surface to aggrade about one channel depth. We use this reworked fraction as the “rate” of production of channel deposits (and destruction of preexisting deposits). The mean aggradation rate of the delta surface is the production rate of overbank material. The rate relationship between reworking and delta aggradation provides a good prediction of the observed amounts of channel and overbank deposits in two experimental alluvial fan deltas. Lastly, we develop a scaling relationship between delta surface reworking rates and channel planform change. This is used to develop a direct relationship between channel mobility in modern field systems and their bulk channel - overbank deposit proportions. With additional work, we hope this type of analysis can be applied to determining probabilities of channel body connectivity, which is important for the extraction of subsurface reservoirs of water and hydrocarbons.