ASBOG Practice Exam

What features characterize an angular unconformity?

1. Flat layers of sediment

2. Complex, tilted underlayers covered by sediments

3. Single, horizontal bedding

4. Perfectly parallel strata

The correct answer is: Complex, tilted underlayers covered by sediments

An angular unconformity is characterized by its distinct relation between tilted or folded layers of rock and the overlying sedimentary layers that are deposited horizontally. The complex, tilted underlayers indicate past geological events, such as tectonic activity, that caused these layers to shift from their original horizontal position. When subsequent sedimentary rocks are deposited on top of these tilted layers, they often remain relatively flat, creating a clear visual contrast that defines the angular unconformity. The presence of these complex, tilted underlayers is crucial for identifying angular unconformities because it reflects significant geological history, including uplift and erosion, followed by new sediment deposition. In contrast, options that refer to flat layers of sediment, single horizontal bedding, or perfectly parallel strata do not align with the definition of an angular unconformity, as they fail to demonstrate the angular relationship that is a hallmark of this geological feature.