In thrust fault systems, a fenster reveals which of the following?

In thrust fault systems, a fenster reveals which of the following?

• A. An eroded area exposing older rocks above the thrust
• B. An eroded area exposing younger rocks beneath the thrust
• C. A fold within the thrust sheet
• D. A fault line within the bedrock

Answer: (B)

A fenster is a window through a thrust sheet that reveals the rocks lying beneath it—the footwall. Erosion removes part of the overlying nappe, exposing what was underneath. Those footwall rocks are typically younger than the rocks that comprise the thrust sheet itself, so the window shows younger rocks beneath the thrust rather than above it or within the thrust sheet. This exposure helps geologists sample the underlying stratigraphy without having to remove the entire thrust.

A fenster is a window through a thrust sheet that reveals the rocks lying beneath it—the footwall. Erosion removes part of the overlying nappe, exposing what was underneath. Those footwall rocks are typically younger than the rocks that comprise the thrust sheet itself, so the window shows younger rocks beneath the thrust rather than above it or within the thrust sheet. This exposure helps geologists sample the underlying stratigraphy without having to remove the entire thrust.