What is a nonconformities?

Answer 1

Nonconformity - n, In geology, an erosional surface on igneous and/or metamorphic rocks that is overlain by younger sedimentary rocks. The erosion surface indicates that the older igneous and metamorphic rocks once were exposed at the surface. Subsequently, they moved downward, were covered with water, and became the foundation for deposits of younger sediemntary rocks.

An nonconformity is a specoial case of the more general term unconformity, which is any discontinuity in the stratratigraphic record.