3D GEOMETRIC MODEL USING STRUCTURE FROM MOTION (SFM) AND KINEMATIC ANALYSIS OF FOLD-THRUST BELT STRUCTURES EXPOSED IN A QUARRY ON THE EAST BANK OF THE SOUTHERN FORK OF SHENANDOAH RIVER IN PAGE VALLEY, VA

The structures along the 3000 km long Appalachian Valley and Ridge are a result of three distinct collisional orogenies (Taconic, Acadian, and Alleghenian). The structures formed during these orogenies are typically easterly dipping thrust faults and upright to inclined fault-related-folds that indicate a westerly vergence of the structures. Mapping done by Patterson and Whitmeyer 2012 in the north-western region of Page Valley, VA indicate the presence of an easterly dipping thrust fault and overturned folds.

Our study area is a quarry located in the southern part of the Patterson and Whitmeyer 2012 study area. The rocks exposed in the quarry are the Ordovician Edinburg Formation. The quarry exposes a recumbent isoclinal fold along the northeastern wall of the quarry and S-type recumbent folds in the northwestern wall of the quarry. Two westerly dipping thrust faults separate the folded structures exposed in the quarry. The purpose of this study is to (a) determine the three-dimensional geometry of the structures in the quarry, (b) determine the development of the sequence of the structures, and, (c) determine how the structures in the quarry relate to the overall structure in the Page Valley, VA.

To determine the three-dimensional geometry of structures in the quarry, images with 70% overlap were taken along the exposed face of the quarry. Several sets of images at different distances were acquired to generate the best fit 3D panoramic model. The images were then processed using Agisoft Photoscan © to develop the 3D panoramic model of the structures exposed in the quarry. Preliminary interpretation of the 3D geometry and field analysis of structural geometries on photo base indicates that the westerly dipping faults in the quarry are likely back-thrusts and the folding in the northwestern wall of the quarry is likely related to the back-thrusts during the Alleghenian Orogeny. Whether the back thrust roots to the easterly dipping fore-thrust to the east of the quarry mapped by Patterson and Whitmeyer 2012, requires further research. Preliminary results from 1:100 scale geologic mapping of the region immediately around and within the quarry support our 3D model.