Question

An unconformity where sedimentary layers are deposited over eroded igneous or metamorphic rocks is called a?

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

Hint:

Nonconformity = Sedimentary rocks over \textbf{non-sedimentary} (igneous/metamorphic) rocks.

Answer 1

The Correct Option is C

Concept: An unconformity represents a gap in the geological record caused by erosion or non-deposition. Different types of unconformities are identified based on the nature of rock layers:

• Angular unconformity: Tilted or folded older rocks overlain by horizontal younger strata.
• Disconformity: Parallel sedimentary layers with a gap in time.
• Nonconformity: Sedimentary rocks overlying igneous or metamorphic rocks.
• Paraconformity: Layers are parallel with no visible erosion surface but represent a time gap.

Step 1:Understand the rock types involved.
The question specifies sedimentary rocks deposited over eroded igneous or metamorphic rocks.
Step 2:Match with the correct unconformity type.
This situation corresponds to a nonconformity.
Step 3:Differentiate from other types.

• Angular unconformity involves tilted sedimentary layers.
• Disconformity involves parallel sedimentary layers.
• Paraconformity has no visible erosion but represents missing time.

Step 4:Conclude the answer.
Thus, the correct answer is nonconformity.