ASBOG Practice Exam

In antiforms, what type of rocks are typically found in the core if the stratigraphic sequence is known?

1. Stratigraphically younger rocks

2. Stratigraphically older rocks

3. Unknown rocks

4. Igneous rocks

The correct answer is: Stratigraphically older rocks

In an antiform, the structure is characterized by an arch-like configuration where the rock layers are bent upward. If the stratigraphic sequence is known, the core of an antiform typically contains stratigraphically older rocks. This is due to the nature of geological folding, where the rocks that are present at the highest position in the structure have been displaced upwards, while the older rocks have been pushed into the center due to tectonic forces. As the layers are folded, any older strata that were originally deposited on the bottom can end up at the core of the antiform, encased by progressively younger layers that have been folded over them. Understanding this gist is crucial for interpreting geological structures and assessing the relative ages of the rock layers involved in fold formations. The other options focus on various possibilities that do not align with the established principles of geology. For instance, stratigraphically younger rocks would be found in the outer layers rather than the core. Unknown rocks would imply a lack of clarity regarding the stratigraphy, which contradicts the premise that the sequence is known. Lastly, while igneous rocks can exist within such structures, the presence of stratigraphically older rocks is a specific feature related to the folding type, making this option the