ASBOG Practice Exam

When observing a plunger fold, what is a distinguishing feature of its map representation?

1. An isolated triangular shape

2. A circular concentric pattern

3. A U-shaped pattern with distinct limbs

4. A series of random lines

The correct answer is: A U-shaped pattern with distinct limbs

In the context of geological structures, a plunger fold, also known as a "chevron fold," is characterized by its distinct U-shaped pattern when represented on a map. This shape is formed as layers of rock are compressed, resulting in the limbs of the fold being oriented in opposite directions, creating a clear and recognizable U formation. The map representation displays these limbs converging toward the same axis, often with sharp, angular features that make the fold stand out. The U-shape of a plunger fold is an important aspect, as it reflects the folding mechanism that often involves layers of rock being pushed upwards and laterally. This particular pattern enables geologists to identify the structural behavior of the rocks and makes it easier to interpret the geological history of the area. In contrast, the other options present features that are not representative of plunger folds. An isolated triangular shape could suggest a different type of geological feature such as a thrust fault, while a circular concentric pattern typically indicates a dome or basin structure. A series of random lines would not convey a consistent geological feature, making it ineffective for identifying specific fold types.