Rapid mangrove sediment accretion in late-Holocene paleochannels of Singapore

Abstract

The evolution of mangroves in response to sea-level rise will partially depend on the availability of accommodation space, which is influenced by the hydrodynamic setting. Here, we reconstruct mangrove evolution in a paleochannel of Sungei Jurong (i.e., Jurong River), Singapore via litho-, bio-, and chrono-stratigraphical analyses. Paleochannels are a commonly-occurring, but under-studied hydrodynamic setting in mangroves. Our results show a stratigraphy of a pre-Holocene basal unit of light grey clayey silt with no recorded microfossils (Unit I), overlain by dark grey clayey silt with 45–58% mangrove pollen (e.g., Rhizophora mucronata, Kandelia candel, and Rhizophora apiculata) and no recorded foraminifera (Unit II). Overlying Unit II is dark brown sandy silt with 44–67% mangrove pollen and no recorded foraminifera (Unit III), separated by a sharp contact from light brown clayey silt (Unit IV) with 39–67% mangrove pollen and agglutinated foraminifera (e.g., Trochammina inflata, Jadammina macrescens, and Haplophragmoides spp.). We develop a Bchron age-depth model from eight radiocarbon dates of plant macrofossils in the form of wood. We infer the presence of a tidal channel near a mangrove environment with a maximum sediment accretion rate of 3.3–5.0 mm yr−1 (~1,230 ± 60 to 990 ± 70 cal. yrs. BP), and an abandoned paleochannel with sediment accretion of up to 18.0–30.0 mm yr−1 (~500 ± 30 cal. yrs. BP to present), separated by a maximum hiatus of 590 cal. yrs. The provision of accommodation space in paleochannels may be driven by rapid sediment accretion caused by overbank flow as well as precipitation and overland flow, thus exemplifying the influence of local hydrodynamics.