THREE-DIMENSIONAL GEOMETRIC MODELING OF THRUST DUPLEX IN THE FEURA BUSH QUARRY, SELKIRK, NY USING STRUCTURE FROM MOTION (SFM)

The Hudson Valley Fold-Thrust Belt (HVB) is a north-south trending, 2-4 km wide region of deformed Silurian through Devonian strata that extends from Kingston, NY to Albany, NY. Mapping along-strike of the HVB indicate a reduction in the deformation intensity towards the north. The Feura Bush Quarry in Selkirk, NY exposes a duplex geometry- the Feura Bush Duplex. This duplex structure is related to the structures in the northern part of the HVB. In this context, the location of an intensely deformed duplex towards the northern end of the HVB is enigmatic. To understand how the Feura Bush Duplex’s position in the northern HVB relates to the deformation along-strike within the HVB, we chose to study the three-dimensional geometry of the duplex. Three nearly perpendicular walls of the quarry expose the internal geometry of the duplex and therefore provide an excellent opportunity to study the three-dimensional geometry of the duplex. Overlapping images for each quarry wall were recorded by a camera on a tripod located at a central location within the quarry. The images were separated into batches for the northern wall, the western wall and the southern wall. The images of each wall were stitched together by AgisoftTM PhotoScan to create a panoramic image for each wall. The panoramic images of each wall were then stitched together to form a final panoramic image of the entire Feura Bush Quarry. The panoramic image of the entire quarry can be rotated freely in any direction to observe the structures exposed in the quarry and was used to develop and study the complete three-dimensional geometry of the duplex exposed in the quarry. In addition to the model developed using AgisoftTM PhotoScan a three-dimensional block model was generated using Fusion 360TM where walls of the quarry were pushed back to expose the three dimensional geometry of the nested duplex in the northern wall and to clearly demonstrate the continuity of the detachment surfaces throughout the quarry. Geometric analysis of the detachment faults exposed along the quarry walls indicate that deformation within this duplex was accommodated along at least three local detachments. The northern and southern walls of the quarry display at least three detachment faults and numerous thrust ramps and thrust-related folds.