ASBOG Practice Exam

In the context of unconformities, which term is used for the unconformity that records missing time and changing geologic environments?

1. Disconformity

2. Angular unconformity

3. Nonconformity

4. Paraconformity

The correct answer is: Angular unconformity

The term that describes an unconformity which records both missing time and changing geologic environments is known as an angular unconformity. An angular unconformity occurs when there are two sets of sedimentary rock layers that have been deposited at different angles. This indicates that there has been a period of erosion or non-deposition between the two layers, as the layers were formed during different geological periods or environments before being uplifted, tilted, and eroded. When observing an angular unconformity, one can clearly see the juxtaposition of older rock layers that were tilted and younger layers that were deposited horizontally on top of them. This distinct angle difference not only shows the significant time gap but also highlights the changing conditions during the time of deposition for the younger layers. In contrast, other types of unconformities each have their own characteristics: a disconformity involves layers that are parallel and separated by an erosion surface, a nonconformity occurs where sedimentary rocks lie on top of older, igneous or metamorphic rocks, and a paraconformity represents a type of disconformity but without any apparent erosion surface or angle of tilting, making it harder to detect the missing time without further detailed examination.