An orthorectified image of a fault propagation fold in the Tuscarora Sandstone near Baker, WV
A classic Suppe Fault Propagation Fold (Suppe and Medwedeff, 1990)
I came across this little gem of a fault propagation fold last year while driving back from Washington DC along Corridor H (Highway 48) in eastern West Virginia.
If you don't know or remember what a fault propagation fold is, it's a thrust-related fold where part of the displacement on the fault goes into faulting new rock ahead of the fault tip, and part of the displacement goes into folding, or bending the layers above the thrust.
If you don't know or remember what a fault propagation fold is, it's a thrust-related fold where part of the displacement on the fault goes into faulting new rock ahead of the fault tip, and part of the displacement goes into folding, or bending the layers above the thrust.
In this particular outcrop, the thrust ramp has propagated along cross beds in the Tuscarora Sandstone. This complicates the classic fault propagation fold geometry that we might see with originally horizontal stratigraphy (as shown in the image above), but it's still a fault propagation fold. What's nice here is that it's possible to match beds that were cut by the thrust and see that displacement decreases toward the fault tip: a diagnostic feature of fault propagation folds. The fault tip is also visible in outcrop.
In the 3D image below, click through the annotations to see how the thrust has propagated up-section. There are several other fault related folds in the view. Can you find them? Try clicking the full screen button on the bottom right for the full view.
(This will work best in Chrome or Firefox, but possibly not as well in Internet Explorer).
In the 3D image below, click through the annotations to see how the thrust has propagated up-section. There are several other fault related folds in the view. Can you find them? Try clicking the full screen button on the bottom right for the full view.
(This will work best in Chrome or Firefox, but possibly not as well in Internet Explorer).
Faulted bed contacts (digitized in the field with binoculars) showing decrease in slip up-section. The fault is in pink, and the cross-beds that form the ramp in the footwall are in black.
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