In geology, a diachronism, or diachronous deposit, is a sedimentary rock formation in which the material, although of a similar nature, varies in age with the place where it was deposited.
Other usages
The term may also be applied to other features that vary in age, such as erosion surfaces, areas of uplift, etc. It is also sometimes applied to fossils which appear sporadically at different times in different places due to migration, though such usage is regarded by some authors as incorrect. ==References==