Beaches and Coasts

Beaches and their deposits occupy a significant proportion of the World's coastlines and are prevalent in the geological record. Modern shorelines are subdivided into erosional vs. depositional features. Erosional or rocky shorelines are more common but are not preserved in the rock record. Depositional shorelines are subdivided based upon the dominant process (waves, tides or rivers) and whether the shoreline is in net progradation or net transgression. Beaches are a key component of wave dominated systems. A typical vertical transect through a wave dominated shoreline succession includes offshore shelf deposits, passing upward through a heterolithic transition zone into the shoreface. The shoreface is comprised of hummocky cross stratified storm deposits overlain by trough cross bedding formed by the migration of bars in the upper shoreface. The shoreface is overlain by the deposits of an inter-tidal foreshore where shoaling waves break. Beaches are a key component of the rock record as they are sensitive indicators of subtle sea-level change. They are also significant reservoirs for hydrocarbons and aquifers for water.