allochthone

Allochthone is a term used in geology and paleontology to describe fossils or rocks that have been transported from their original place of formation or life to a different location. The word itself derives from the Greek words "allos" meaning "other" and "chthon" meaning "earth." Therefore, an allochthonous body is essentially an "other earth" or a foreign mass.

In geology, allochthonous rocks are typically found in large thrust sheets or nappes, which are massive blocks of rock that have been moved significant distances, often for many kilometers, over the Earth's surface due to tectonic forces such as continental collision. These displaced rock masses may be composed of different geological formations or even entirely different terranes than the underlying autochthonous rocks. Identifying allochthonous units is crucial for understanding the tectonic history and structural evolution of a region.

In paleontology, allochthone refers to fossil specimens that are found in a sedimentary layer different from the one in which the organism originally lived and died. This can occur through various processes, including river transport, glacial action, or even mass wasting events that carry deceased organisms to a new depositional environment. The study of allochthonous fossils can provide insights into past environments, transport mechanisms, and the fidelity of the fossil record. It is important to distinguish between allochthonous and autochthonous fossils, the latter being those found in the stratum where they originally lived.