WIDE VERTICAL FRACTURES IN THE CHAUMONT LIMESTONE IN JEFFERSON COUNTY, NY: GLACIAL ORIGIN OR TECTONIC ORIGIN?

There are populations of up to 30 cm-wide, near vertical fractures in limestone pavement of the Chaumont Formation exposed in the moderately vegetated Chaumont Barrens Preserve in Chaumont, New York. Although the common view attributes the fractures to glacial loading, the presence of local deformation structures suggests a potential tectonic origin. In order to determine the responsible mechanism, we quantify the collective orientation and total length of the well-developed fractures in the whole study area, using LIDAR (light detection and ranging) elevation data. The LIDAR data are analyzed with a computer algorithm we developed to locate data points that potentially fall on the bottom of a fracture. Each linear cluster of data points is detected as a fracture, the orientation and length of which are measured. Our result reveals three distinctive fracture sets: NE-SW (~045˚), ENE-WSW (~070˚), and SE-NW (~125˚). The pair of fracture sets of 070˚ and 125˚ (2θ = 110˚) appear to be the only conjugate fracture set that is physically possible based on the Coulomb fracture criterion, which points to a tectonic origin of the fractures. The third NE-SW fracture population may have resulted from a change in the local stress field; only ~13˚ of a counterclockwise rotation of the horizonal σ₁ could cause the 045˚ fracture population. The post-rotation horizontal σ₁ orientation agrees with the maximum horizontal stress around Lake Ontario proposed by a previous study. The orientation of the NE-SW fracture population is consistent with the strike of the local, near vertical faults.