From apex to shoreline: fluvio-deltaic architecture for the Holocene Rhine-Meuse delta, The Netherlands

Abstract

Despite extensive research on alluvial architecture, there is still a pressing need for data from modern fluvio-deltaic environments. Previous research in the fluvial-dominated proximal and central Rhine-Meuse delta (The Netherlands) has yielded clear spatial trends in alluvial architecture. In this paper, we include the backwater length to establish architectural trends from apex to shoreline. Channel-belt sand body width/thickness ratios and interconnectedness were determined and the proportions of fluvial channel-belt deposits, fluvial overbank deposits, organics and intertidal deposits were calculated for the complete fluvio-deltaic wedge, based on high-resolution geological cross-sections. It was found that the average width/thickness ratio of channel-belt sand bodies in the proximal delta is five times higher than in the distal delta. Other down-valley trends include an 80 %-decrease of the channel deposit proportion (CDP) and a near-constant proportion of overbank deposits. Additionally, interconnectedness in the proximal delta is three times higher than in the distal delta. Based on the Rhine-Meuse dataset, the authors propose a linear empirical function to model the spatial variability of CDP. It is argued that this relationship is driven by four key factors that change along stream: channel lateral-migration rate, channel-belt longevity, creation of accommodation space and inherited flood-plain width. Additionally, it is established that the sensitivity of CDP to changes in the ratio between channel-belt sand body width and flood-plain with, (normalised channel-belt sand body width) varies spatially and is greatest in the central and distal delta. Also, the proportion of fluvial channel-belt sands is generally an appropriate proxy for the total sand content of fluvio-deltaic successions, albeit that its suitability as a total-sand indicator rapidly fades in the distal delta. With this paper, unique high-resolution quantitative data and spatial trends on the alluvial architecture are available for an entire delta, hereby providing a dataset that can be used to further improve existing fluvial stratigraphy models.