1. A surface that separates younger strata from eroded, dipping, older strata and represents a gap in the geologic record.
2. Structural discordance of stratified rocks produced by erosion of the older beds and deposition of younger beds on the edges of the eroded rocks.

Angular unconformities signify deformation of the older strata prior to deposition of the younger ones.

They may be simulated by cross-bedding and by faulting, distinction of which from angular unconformities generally is recognized easily by various criteria.