Bioclastic

Bioclastic is a term used in geology to describe sedimentary rocks or rock textures that are composed predominantly of fragments produced by living organisms. These grains are typically skeletal debris from calcareous organisms such as mollusks, brachiopods, foraminifera, corals, bryozoans, echinoderms, and algal fragments. The term is most commonly applied to carbonate rocks but can also describe clastic rocks in which biogenic material makes up the majority of the clasts.

Bioclastic rocks form from the accumulation and subsequent lithification of biogenic debris in marine environments where biological activity is high. After deposition, compaction and cementation turn the loose sediment into solid rock. This process yields rocks such as bioclastic limestones or bioclastic dolostones, and, in some cases, bioclastic sandstones if finer skeletal fragments are present.

Common examples include fossiliferous limestone, which contains abundant shell and skeletal fragments, and coquina, a coarse, shell-dominated sediment that can range from unconsolidated to loosely compacted rock. In carbonate classifications, textures described as bioclastic may appear as fossil-rich packstones or wackestones, indicating varying degrees of grain support and matrix.

The term aids in interpreting past environments, often pointing to shallow, warm, marine settings with abundant life and relatively high sedimentation rates. While bioclastic materials are derived from living organisms, the broader categories of biogenic or biochemical rocks describe other ways organisms influence sediment formation, making bioclastic a specific descriptor of biogenic debris as clastic components.