12.1: Review of unconformities and other types of contacts
- Page ID
- 20965
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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 deposited atop crystalline rocks that formed at depth.
Disconformity – occurs when you have sedimentary atop sedimentary with no obvious angular discordance. The unconformity surface can have significant amounts of erosional relief.
Figure \(\PageIndex{1}\): Diagram showing the three types of unconformities as well as different types of igneous contacts and a variety of expressions of a fault contact (Page Quinton via Wikimedia Commons; CC BY-SA 4.0).