This unconformity is formed where sedimentary beds overlie an erosional surface carved into igneous or metamorphic rocks?

This unconformity is formed where sedimentary beds overlie an erosional surface carved into igneous or metamorphic rocks?

• A. Disconformity
• B. Angular Unconformity
• C. Nonconformity
• D. Paraconformity

Answer: (C)

Unconformities indicate a gap in the geological record. When sedimentary beds sit on top of an erosional surface that cuts into igneous or metamorphic rocks, the feature is a nonconformity. The key idea is a basement of crystalline rocks eroded before new sediment accumulated, creating a clear break between the non-sedimentary foundation and the overlying sedimentary sequence. This differs from angular unconformity, where the underlying and overlying rocks are both sedimentary but misaligned due to tilting or folding before erosion and re-deposition. A disconformity occurs within sedimentary rocks with parallel bedding but a missing time interval, and a paraconformity is a subtle unconformity with little obvious erosion or relief. The scenario described is the classic case of nonconformity.

Unconformities indicate a gap in the geological record. When sedimentary beds sit on top of an erosional surface that cuts into igneous or metamorphic rocks, the feature is a nonconformity. The key idea is a basement of crystalline rocks eroded before new sediment accumulated, creating a clear break between the non-sedimentary foundation and the overlying sedimentary sequence. This differs from angular unconformity, where the underlying and overlying rocks are both sedimentary but misaligned due to tilting or folding before erosion and re-deposition. A disconformity occurs within sedimentary rocks with parallel bedding but a missing time interval, and a paraconformity is a subtle unconformity with little obvious erosion or relief. The scenario described is the classic case of nonconformity.