Unconformities

Unconformities-very long times of nondeposition and/or erosion, of which there are three basic types.

• disconformity- surface(erosion) seperating younger from older rocks. These rock layers are horizontal (parallel) to each other.
  
• nonconformity- erosion surface that separates old metamorphic rocks from younger sedimentary rocks.
• angular unconformity- tilted sedimentary rocks that are overlain by younger flat-lying sedimentary rocks.

Cross-cutting principle- the intrusive rock body is younger than the rocks it cuts. You cannot cross-cut rock layers if they are not already present.

Principle of inclusions- inclusions or fragments in a rock are older than the rock itself.