Abstract
Understanding river response to changes in relative sea level (RSL) is essential for predicting fluvial stratigraphy and source-to-sink dynamics. Recent theoretical work has suggested that rivers can remain aggradational during RSL fall, but field data are needed to verify this response and investigate sediment deposition processes. We show with field work and modeling that fluvio-deltaic systems can remain aggradational or at grade during RSL fall, leading to superelevation and continuation of delta lobe avulsions. The field site is the Goose River, Newfoundland-Labrador, Canada, which has experienced steady RSL fall of around 3–4 mm yr –1 in the past 5 k.y. from post-glacial isostatic rebound. Elevation analysis and optically stimulated luminescence dating suggest that the Goose River avulsed and deposited three delta lobes during RSL fall. Simulation results from Delft3D software show that if the characteristic fluvial response time is longer than the duration of RSL fall, then fluvial systems remain aggradational or at grade, and continue to avulse during RSL fall due to superelevation. Intriguingly, we find that avulsions become more frequent at faster rates of RSL fall, provided the system response time remains longer than the duration of RSL fall. This work suggests that RSL fall rate may influence the architecture of falling-stage or forced regression deposits by controlling the number of deposited delta lobes.
Highlights
Predicting how rivers erode or deposit sediment in response to relative sea-level (RSL)change is critical for understanding sequence stratigraphy (Catuneanu, 2006) and source to sink dynamics (Romans and Graham, 2013)
This idea was quantified by Muto and co-workers (Muto and Steel, 2002, 2004; Muto and Swenson, 2005, 2006; Swenson and Muto, 2007) who showed that a fluvio-deltaic system will not incise when RSL falls if the fluvial response time τ is longer than the duration of RSL
River delta and Delft3D simulations, we have shown that fluvial avulsions can occur during RSL
Summary
Predicting how rivers erode or deposit sediment in response to relative sea-level (RSL). Our goal here is to understand the processes that control sediment deposition during RSL fall by combining elevation analysis, and optically stimulated luminescence (OSL) data from the modern Goose River, Newfoundland-Labrador, and morphodynamic modeling. Our observations show that as RSL falls Goose River avulsions create multiple delta lobes at progressively lower elevations. To constrain the timing of fluvio-deltaic deposition on the Goose River, we conducted a topographic analysis using 30-m shuttle radar topography mission (SRTM) data and collected sediment cores for OSL dating from delta lobes B and C (Fig. 1). Our OSL results and topographic analysis shows that during RSL fall the Goose River avulsed to create at least three delta lobes at progressively lower elevations (Fig. 1 inset). Avulsion number increases with RSL fall, until a point is reached and they decline rapidly (Figure 2D)
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