Environmental Engineering Reference
In-Depth Information
Fig. 2.5
On many coasts sand drifted shoreward from sea floor shoals during the Late
Quaternary marine transgression (
a
), and for a time after this transgression ended (
b
), so that
beaches prograded. With the attainment of a smooth concave sea floor profile progradation
ceased (
c
), and the landward migration of this profile resulted in beach erosion and coastline
retreat (
d
). © Geostudies
Sediment supply from the sea floor is also seen where shells, or other biogenic
particles derived from sea floor organisms, become calcareous sand and gravel
that drifts shoreward to be added to beaches. Several beaches on the west coast of
Western Australia are still maintained in this way, supplied with calcareous sand
and gravel from disintegrating nearshore reefs of dune calcarenite (which consists
of sand, usually mainly calcareous, cemented by precipitated carbonates to form a
coherent sandstone).
Such beaches prograde, or are maintained, as long as there is a supply of sea
floor sediment, but beach erosion develops if the sediment supply is reduced
