Which feature is most likely to expose younger rocks beneath the thrust sheet?

• A. Fenster
• B. Syncline
• C. Anticline
• D. Monocline

Answer: (A)

Fenster, or window, is an opening in a thrust sheet that unroofs rocks lying beneath it. In a thrust belt, erosion or tectonic removal of part of the overlying sheet can create a window, so you can directly see the rocks that lie beneath the thrust sheet. If those underlying rocks are younger than the sheet, this window will expose younger material. The other options describe folds or bends in layered rocks (syncline, anticline, monocline) and do not by themselves produce an exposure through the thrust sheet to reveal underlying units. So the window is the feature that best explains exposing younger rocks beneath the thrust sheet.