ASBOG Practice Exam

What outcrop pattern results when gentle folding in sedimentary rocks is recognizable?

1. Concentric or sub-concentric

2. Linear

3. Radial

4. Vertical

The correct answer is: Concentric or sub-concentric

The outcrop pattern that emerges from gentle folding in sedimentary rocks is typically concentric or sub-concentric. This occurs because gentle folds create curved layers of rock that can manifest at the surface in a circular or oval pattern. In such formations, the innermost layers, or those closest to the fold axis, are often younger than the outer layers due to the nature of the folding process, which involves the compression of layers, causing them to buckle and bend. In stratigraphic terms, this results in the youngest rocks being exposed in the center of the fold and progressively older rocks appearing towards the outer edges. This pattern is distinctively seen in geological features such as anticlines and synclines, where the bending of rock layers dictates how they are exposed at the surface. Concentric patterns are a hallmark of such geological formations, making this option the most representative of the effects of gentle folding on outcrop appearance.