bioklastik

Bioklastik, also known as bioclastic, describes a sedimentary rock texture that is dominated by biogenic skeletal fragments. These fragments originate from organisms such as shells and skeletons of mollusks, bryozoans, foraminifera, echinoderms, and corals, which have been weathered, dissolved, or broken and then redeposited or re-cemented into the rock. The term can apply to both carbonate rocks (limestones and dolostones) and, less commonly, siliciclastic rocks when biogenic fragments are a major component.

Bioclastic rocks form in marine settings where calcareous or siliceous organisms accumulate faster than they are reworked or dissolved. This accumulation can occur on beaches, shallow shelves, reef fronts, and lagoonal environments. Over time, the accumulated bioclasts are compacted and cemented, producing a coherent rock. Diagenetic processes, including cementation by calcite or silica, can enhance the stability of the material and preserve the bioclastic texture.

In petrography, bioclastic rocks are described by the abundance and types of biogenic fragments. They are commonly found in limestone and dolostone sequences and can range from mud-supported to grainy textures. Common examples include coquina (predominantly loose shell fragments that have lithified into a rock) and fossiliferous limestone (rich in visible fossils and shell debris), as well as chalk, which consists largely of microscopic biogenic remains.

Bioklastik provides important clues about past marine environments, biological productivity, and diagenetic history, helping geologists interpret ancient climate, sea level changes, and sedimentary dynamics.