Local Versus Regional Controls on the Morphology and Texture of Preserved Beach and Foredune Ridges

Beach-and-foredune-ridge plains archive paleoenvironmental changes within their morphology and stratigraphy. Despite advances in integrating modern process data with coastal sedimentary archives, we lack a quantitative understanding of how coastal progradation processes such as time-varying wave, current, and sediment transport processes impact stratigraphic and morphologic records. To address this gap, we pair geophysical, sedimentological, and morphological data with hydrodynamic and sediment-transport modeling to understand the processes impacting paleoenvironmental archives (e.g., beach slopes, grain size, and morphology) in four beach-ridge plains along Virginia's coast (USA). We quantify these processes at three periods (800 CE, 1880 CE, and modern) using Delft3D model grids derived from stratigraphic, historical, and modern bathymetric data. We hold model boundary conditions consistent across scenarios to focus on local (kilometer-scale) physical processes driving ridge morphology and architecture. Key differences among the ridge plains are primarily related to orientation with respect to regional wave conditions; specifically, beachfaces are steeper and coarser on ridge plains formed by shore-parallel spit-elongation compared with those formed through cross-shore progradation. Model results show modest differences in sediment-transport patterns and fluxes over the last 1200 years; present-day and historical spits and inlets trap medium and coarse sand, resulting in finer sediments reaching downdrift barriers and attendant shallower beachfaces. Spatial variations in beach-ridge stratigraphy and morphology remain consistent through time, indicating that at this site, beach-ridge archives reflect primarily local forcings. This work offers an example of how to cautiously interpret beach-ridge stratigraphic and morphological records.