STRUCTURAL ANALYSES OF A RE-EXPOSED ROADCUT NEAR BERGTON, VA: USING MODERN IMAGING TECHNIQUES TO RE-EVALUATE DEFORMATION

A 20m by 72m road cut near Bergton, Va was re-blasted in 2010 when Bergton Rd. (Va. Rt. 820) was widened. The road cut on the north side of Bergton Rd. consists of centimeters to meters thick beds of finely grained sandstone and mudstone of the Greenland Gap group, crosscut by multiple thrust faults with associated folds. The highly deformed outcrop was previously sketched and analyzed in a 1985 thesis by V. S. Mandros. In 2010 VDOT blasted about 2 meters into the hillside, producing a fresh cut with an improved exposure of structural features. The new surface shows a greater amount of macro low-angle thrust faults, high-angle thrust faults, and larger folded segments. The cut also exposes faults that were not documented in 1985. The original 1985 sketch extended for 47 meters along the road, while the newly exposed road cut has obvious deformation that extends horizontally for 72 meters along the road.

We have reanalyzed the road cut, using new imaging techniques to capture, in detail, the newly exposed structural features. Approximately 20 high-resolution images were photographed with a high-powered digital SLR camera to create a photo mosaic of the outcrop showing details of each fold and fault. We used this image to construct a new detailed sketch of structural elements. Features that were found during analyses of the new outcrop were a new 11m-long low-angle thrust fault, and four previously undocumented folds. Not only does the newly exposed Bergton road cut give insight into how this region of the Appalachian Mountains was created during the Alleghanian Orogeny, but it also allows for a re-evaluation of observations and interpretations made in 1985. The new outcrop re-affirms previous measurements of shallow southeastern dips of the faults and northwestern fold vergence and movement along the faults. This approach to comparing past observations and interpretations with new analyses based on modern imaging technology enhances our ability to understand and interpret structural deformation and the tectonic history of an area.