An outcrop pattern comprised of parallel zig-zag contacts on a geologic map represents what kind of structure?

• A. Horizontal bedding
• B. Faulted surfaces
• C. Plunging anticlines and synclines
• D. Nondeformed strata

Answer: (C)

Reading geologic maps, a pattern of parallel zig-zag contacts signals that the rock beds are folded with a dipping hinge line. When beds are arranged in plunging anticlines and synclines, the surface trace of each bed’s contact shifts direction as you move across the fold, producing a sawtooth or zig-zag appearance that runs roughly parallel in plan. This is different from horizontal bedding, which would give smooth, straight, parallel contacts; faulted surfaces, which would show breaks and offsets along faults; or nondeformed strata, which would lack any zig-zag deformation pattern. So the zig-zag parallel contacts indicate plunging anticlines and plunging synclines.