Abstract
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 5 times higher than in the distal delta. Other down-valley trends include an 80 % decrease in the channel deposit proportion (CDP) and a near-constant proportion of overbank deposits. Additionally, interconnectedness in the proximal delta is 3 times higher than in the distal delta. Based on the Rhine–Meuse dataset, we propose a linear empirical function to model the spatial variability of CDP. It is argued that this relationship is driven by four key factors: channel lateral-migration rate, channel-belt longevity, creation of accommodation space and inherited floodplain width. Additionally, it is established that the sensitivity of CDP to changes in the ratio between channel-belt sand body width and floodplain width (normalized channel-belt sand body width) varies spatially and is greatest in the central and distal delta. Furthermore, the proportion of fluvial channel-belt sands is generally an appropriate proxy for the total sand content of fluvio-deltaic successions, although its suitability as a total sand indicator rapidly fades in the distal delta. Characteristics of the backwater zone of the Rhine–Meuse delta are (1) sand body width / thickness ratios that are lower as a consequence of channel narrowing (not deepening), (2) a rapid increase and then a drop in the organic proportion, (3) an increase in the total sand proportion towards the shoreline, and (4) a drop in the connectedness ratio. For this paper, unique high-resolution quantitative data and spatial trends of the alluvial architecture are presented for an entire delta, providing data that can be used to further improve existing fluvial stratigraphy models.
Highlights
The architecture of fluvio-deltaic successions has been studied extensively in the past decades mainly because of the occurrence of valuable natural resources within strata of fluvio-deltaic origin (e.g. Tye et al, 1999; Ryseth, 2000; Kombrink et al, 2007)
With this paper we aim to (1) present new alluvialarchitecture data from the distal Rhine–Meuse delta, (2) discuss the observed trends with specific attention to those in the backwater zone, and (3) develop a function that describes the delta-wide spatial trend in channel deposits (CDP) based on the Rhine–Meuse dataset to be used in the Rhine–Meuse delta and potentially in other deltas as well
The downstream-decreasing trend in channel-belt sand body width / thickness ratio, as established for the proximal and central Rhine–Meuse delta (Gouw, 2008), more or less continues in the distal delta (Fig. 5; note that shown bandwidths represent min–max values, not confidence intervals)
Summary
The architecture of fluvio-deltaic successions has been studied extensively in the past decades mainly because of the occurrence of valuable natural resources (water, hydrocarbons, precious metals, sand) within strata of fluvio-deltaic origin (e.g. Tye et al, 1999; Ryseth, 2000; Kombrink et al, 2007). The architecture of fluvio-deltaic successions has been studied extensively in the past decades mainly because of the occurrence of valuable natural resources (water, hydrocarbons, precious metals, sand) within strata of fluvio-deltaic origin Tye et al, 1999; Ryseth, 2000; Kombrink et al, 2007). Alluvial architecture describes the proportion, distribution and geometry of fluvial sediment bodies in sedimentary basins (Allen, 1978). Alluvial-architecture studies primarily focus on the geometry of fluvial sand bodies (see Gibling, 2006, for an extensive overview), the proportion of channel-belt sands within fluvial successions Ryseth et al, 1998; Bridge et al, 2000; Flood and Hampson, 2015; Blum et al, 2013) and controlling factors reckoned to influ-. Despite the elaborate work that has already been done, there are still two aspects of interest concerning alluvial-architecture research
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