Bioclast

Bioclasts are skeletal fragments of marine or land organisms that are found in sedimentary rocks laid down in a marine environment—especially limestone varieties, some of which take on distinct textures and coloration from their predominate bioclasts—that geologists, archaeologists and paleontologists use to date a rock strata to a particular geological era.

Bioclasts used for such relative dating purposes can be whole fossils or broken fragments of organisms. Their preponderance can give a rough guide to life diversity in the historic biosphere, but absolute counts much depend on water conditions such as the depth of the deposition, local currents, as well as wave strength in large body of water such as lake.