Aeolian Dune Deposits
Growth of a coastal dune is initiated where wind-blown sand is dropped. As the sands build up, a steep leeward slope (foreset) is formed. The angle at which sand will rest without avalanching depends on the nature and the dampness of the sand grains. For sand dunes in Bermuda, the angle or repose is about 35 degrees.
Foresets are seen as parallel dipping beds throughout Bermuda. They generally dip away from the source-beach.
A dune ridge is composed of numerous coalesced dune bodies. The composite structure is implied by the hummocky topography of dune ridges and the accurate pattern of foreset orientations. Each of the many foreset arcs within a ridge represents an individual mound-shaped dune.
The bedding on the windward face, known as backsets or windward beds, varies from parallel, gently inclined layering to low angle, sometimes festooned or wavy cross-bedding.
Erosion of the early dune structure by the wind and movement
of sand on the windward face, result in truncation of foresets by windward
beds. Typically, the truncation surface is planar and gently inclined.
It is a sedimentary feature which is characteristic of Bermuda's limestone