Interlayer slip and joint localization in the East Kaibab Monocline, Utah: field evidence and results from numerical modelling

Abstract

Abstract The mechanics of deformation in multilayer flexures is analysed by comparing field observations of joint clusters from the East Kaibab Monocline, Utah with fracture patterns produced in analytical and numerical experiments. Dune boundaries (bedding planes) were mapped through the thickness of the aeolian Navajo Formation, and the occurrence of joints related to dune boundary slip and fold curvature was documented. Slip along dune boundaries, as evidenced by joint clusters oblique to bedding, occurs along the steep limb of the fold and in the middle of the Navajo. Joints perpendicular to bedding and parallel to the fold axis occur near the synclinal hinge. Numerical experiments examine a layer flexed to match the Navajo at Hackberry Canyon with both uniform and observed distribution of dune boundaries. Within the numerical experiments, horizontal frictional interfaces slip within the centre of the layers where dips are steepest, and opening-mode fractures related to curvature form within the anticlinal and synclinal hinges of the fold. Thus, the first-order numerical results match field observations. This study illustrates the important roles of mechanical stratigraphy and interlayer slip in multilayered folding and the contribution of bedding-plane faults and fold curvature in the production of joint clusters.