shellbearing

Shellbearing describes rocks or sediments in which a substantial portion of the material consists of shells or shell fragments produced by calcareous marine organisms. The term is used in geology, paleontology, and archaeology to characterize composition rather than origin, and may apply to beds, layers, or entire rock types that host abundant bioclasts.

Shellbearing deposits form where dead shells accumulate faster than they are dissolved or eroded, typically in shallow, nearshore settings such as beaches, lagoons, tidal flats, and reefs. Accumulations can appear as shell beds, coquinas, or fossiliferous limestones, and may range from fine-grained muds to coarse, clast-rich deposits.

The principal constituents are calcareous shells of mollusks, brachiopods, echinoderms, and foraminifera, with diagenetic alteration possibly altering original aragonite to calcite and cementing shells together with calcite or silica. Textures include shell-rich, clast-supported beds and calcarenites dominated by sand-sized bioclasts.

Shellbearing records are valuable for paleoenvironmental reconstruction and stratigraphy. The assemblage and preservation of shells provide clues to past salinity, temperature, water depth, and energy conditions. Analyses of shell isotopes and morphologies can inform climate interpretations; in archaeology, shell-rich layers may reflect resource use or trade.

Related terms include fossiliferous limestone, bioclastic limestone, and coquina. The label is descriptive and may be used alongside more specific lithologies.