Bioclastic Sediment

Bioclastic sediment is clastic sediment built mainly from the broken skeletal fragments of marine organisms: shell debris, coral and coralline-algae fragments, foraminifera tests, echinoid plates, and bryozoan pieces. It is the dominant grain type on tropical carbonate platforms and reef aprons, where calcium carbonate production is biological rather than detrital. Grain size spans the Wentworth scale from carbonate mud through skeletal sand to rudstone-grade gravel, and the assemblage records the producing community. Unlike siliciclastic quartz sand, bioclastic grains are intrabasinal, formed in place, so their abundance tracks reef and lagoon productivity rather than river input.