Comparative fracture of joints that strike parallel to structures in sedimentary rocks - Characterization and implications

While cross structure (fold) joints known as F₁ joints in sedimentary rocks, which are approximately parallel to the maximum paleo-principal stress, have received much attention by authors, investigations of strike-parallel joints, F₂ joints, are considerably scantier. It turns out that in two fracture provinces, the Middle Eocene chalks from the Be'er Sheva syncline, Israel, and the Jurassic sandstone at Zion National Park, Utah, USA, there is a far greater ubiquity of strike-parallel multilayer joints than cross structure joints, suggesting that in these provinces the tensile stresses creating F₂ joints were significantly more effective than the orthogonal tensile stresses forming F₁ joints.