ASBOG Practice Exam

Which type of unconformity is characterized by parallel strata and a bedding plane as the contact?

1. Disconformity

2. Angular unconformity

3. Nonconformity

4. Paraconformity

The correct answer is: Paraconformity

The correct answer is characterized by the presence of parallel strata above and below the unconformity, indicating a significant amount of geological time has passed with no deposition of sediments. This type of unconformity does not involve any tilting or folding of the rock layers, which sets it apart from other types. In a paraconformity, the layers maintain a consistent orientation, making the bedding planes appear parallel at the contact point. This type of unconformity can often be challenging to identify in the field because there is little to no visible evidence of erosion or disturbance between the layers. In contrast, an angular unconformity features tilted or folded layers below the unconformity that are not parallel to the overlying layers, showcasing a history of tectonic activity. A nonconformity occurs when sedimentary rocks overlay crystalline rocks, illustrating a significant change in rock types and often a gap in the geological record. A disconformity, while also featuring parallel layers, typically involves erosion or a gap in the sedimentation process that can be seen in the relationship, which differs from the more subtle characteristics of a paraconformity.