Autochthon (geology)

It can be described as rooted to its basement rock as opposed to an allochthonous block or nappe which has been relocated from its site of formation. Autochthonous sediment is sediment found at or very close to its site of deposition.

While an autochthon may have experienced some minor shifting, an allochthonous block will have moved at least a few kilometres. If an overlying allochthon has an opening or hole which exposes the underlying autochthonous material, the hole is called a window or fenster.