Bioclastic sediments include carbonate rich sediments consisting of shell and calcareous algae (shell sand) in the coastal zone, and carbonate rich sediments on the continental shelf, often around coral reefs.
Bioclastic sediments can vary in grain size, from clay to blocks, and have various areas of origin. Locally deposited Bioclastic sediments found near coral reefs most often consist of corals and blocks of dead corals but these sediments may also contain a significant amount of clay, silt and sand that has been transported with the ocean currents. Maps of bioclastic sediments do not contain information about the proportion of living and dead organisms, nor is there information about the species types.
Bioclastic sediments are mapped using the acoustic methods (bathymetry and backscatter provided from multibeam echosounder and sonar), sediment sampling and video surveys.