Rock the ASBOG Exam 2025 – Dig Deep into Geology Greatness!

The term that describes an unconformity where the older surface remains horizontal during non-deposition is a disconformity. A disconformity occurs when there is a significant gap in the geological record, often due to erosion or a lack of sedimentation, but the strata above and below the unconformity are parallel, indicating that the older layers have not been disturbed or tilted after their deposition.

In this scenario, the horizontal older surface signifies the continuity of time during which erosion or non-deposition has taken place without disturbing the original horizontal orientation of the sedimentary layers. This phenomenon is critical in understanding geological history, as it highlights periods of erosion or subaerial exposure that occurred without significant tectonic action.

Other unconformities, such as angular unconformities or nonconformities, involve more complex relationships, such as tilted layers meeting horizontal layers or the juxtaposition of sedimentary layers against igneous or metamorphic rocks, respectively. Paraconformities, on the other hand, suggest a hiatus without any visible surface disease but are indexed through other means rather than the clear horizontal nature seen in disconformities.