Stratigraphy, evolution and morphology of a sand-rich shoreface.

Shoreface morphology and stratigraphic evolution are poorly documented along most of the world's coasts yet are acknowledged to be important influences on shoreline behaviour during changing sea levels. A wide, low gradient, wave-dominated shoreface characterises the area off Xai-Xai in southern Mozambique. It is developed on a Holocene wave ravinement surface cut into deltaic sands punctuated by lithified aeolianite ridges. The 2 km-wide mobile shoreface sand body extends to −23 m depth and averages 10 m in thickness. The modern shoreface bathymetry mimics the underlying wave ravinement surface and this, in turn, is influenced by the presence of aeolianite ridges that create a pronounced break in slope that defines the base of the modern shoreface. The aeolianite influences the wave ravinement profile from which the modern bathymetry is inherited. Comparison with theoretical equilibrium shoreface profile models reveals contrasting shoreface morphodynamic state conditions, dependent upon the model chosen. Based on the model better suited for the lower shoreface. These results emphasize the widely acknowledged but still poorly understood role of geologic inheritance on shoreface morphodynamics and geomorphological evolution, even in sand-rich environments.