Algal mounds
are composed of limestone. They develop as algae grow together as
‘mats’ of slime on the bed of shallow, tropical seas. These
algae can bind calcium carbonate debris (for example, very small fragments
of coral) by trapping the material and eventually growing over it.
Over time, this process can build up a laminated mound of calcium
carbonate or limestone.
Other organisms, such as corals,
may later colonise this mound and grow on top of the algae.
