Influence of organics and clastic lake fills on distributary channel processes in the distal Rhine–Meuse delta (The Netherlands)

Abstract

Organic–clastic lake fills, which include lacustrine deltas, are prominent architectural elements in the distal zone of delta plains. We hypothesize that lakes and fossil lake fills affect the development of a fluvial distributary channel. To test this hypothesis, a Holocene palaeogeographic reconstruction is presented of the Angstel–Vecht area, The Netherlands based on a geomorphogenetic map, lithogenetic cross sections, microfossil analyses, and various dating methods (i.e. 14C-dating, OSL dating, pollen analyses and archaeological evidence). We found that peat accumulation on the Pleistocene substratum started ~ 8000 cal yr BP in response to base-level driven groundwater-level rise. Peat-bounded lakes existed in which gyttja was formed. Fluvial sedimentation in the study area commenced when a new Rhine distributary – the Angstel–Vecht – formed ~ 2970 cal yr BP. As a result, the lakes were filled with fluvially supplied clastic material. Fluvial activity diminished after ~ 2300 cal yr BP although the system continued to function as a high-discharge spillway for Rhine distributaries. This study illustrates the influence of lakes and lake fills on fluvial architecture and sedimentology. Downstream of a lake, levee deposits are thin compared to upstream reaches and the channel-belt sediment is clayey. Furthermore, channels maintain a meandering pattern when organic–clastic lake fills form the substrate because of the relative low bank stability. This is in contrast to straight channels in the distal delta plains that are influenced by erosion-resistant peat substrate.