Which statement best describes an unconformity?

• A. A break in the geologic record caused by erosion or non-deposition
• B. A surface of continuous deposition
• C. A stratigraphic boundary with no break
• D. A volcanic intrusion

Answer: (A)

An unconformity marks a missing interval in the geologic record. It occurs when deposition pauses or erosion removes previously formed material, leaving a surface that separates older rocks from younger ones. This hiatus is exactly described as a break in the geologic record caused by erosion or non-deposition. Different forms—angular, disconformity, or nonconformity—all show this time gap, even though the rocks on either side may be oriented differently or composed of different materials. The other scenarios describe continuous deposition, a boundary with no time gap, or a volcanic intrusion, none of which capture the essential hiatus that defines an unconformity.