👉 Plagioclastic is a biological classification that describes organisms that have a fossil record of organic material. This class includes clams, oysters, barnacles, and other marine invertebrates that are known to have been deposited on or near bodies of water over millions of years. In the context of archaeology, plagioclastic fossils can be found in stratigraphic layers called "plagioclast" or "plagiocrusts." These are small, granular deposits made