12.1: Review of unconformities and other types of contacts
Although we are likely dealing only with disconformities when talking about sedimentary rocks and stratigraphic relationships, its worth remembering that there are three types of unconformities:
Angular unconformity – occurs when there is a marked discordance between layers caused by a period of uplift and erosion during unconformity development.
Nonconformity – occurs when you have sedimentary rocks deposited atop crystalline rocks that formed at depth.
Disconformity – occurs when you have sedimentary rocks atop sedimentary rocks with no obvious angular discordance. The unconformity surface can have significant amounts of erosional relief.