uh-LOK-thuh-nuhs · Originating somewhere other than the place where it is found. In ecology, it distinguishes material entering an ecosystem from material produced within it. An original example: “The stream’s allochthonous carbon came from leaves falling off the surrounding trees.” The stream is carrying resources made on land. Geologists use the same word for rocks or deposits displaced from their place of formation. Pronunciation and geological sense · Ecological sense: USGS