FAULTS
Faults are quite common in orogenic belts. Faults are defined as fractures in rocks along which differential displacement has occurred. Dip-slip faults are those involving movement of rocks in non-horizontal directions. Strike-slip faults involve movement of rocks in horizontal directions.
The two common types of dip-slip faults are normal faults and reverse faults. Small-scale examples of each are shown below.
Normal fault (above & below; cross-section view; field of view: 3.1 cm across) in hard, argillaceous limestone (Silurian). Normal faults result from extensional stress, and involve downward movement of the hanging wall and upward movement of the footwall.
Locality: beach cobble from shoreline at western end of South Bass Island, western Lake Erie, northern Ohio, USA.
Reverse fault (above & below; cross-section view; field of view: 2.4 cm across) in finely-laminated rock gypsum (Castile Formation, upper Upper Permian). Reverse faults result from compressional stress, and involve upward movement of the hanging wall and downward movement of the footwall.
Locality: loose talus from State Line outcrop - roadcut along Rt. 82/Rt. 180, between Guadalupe Mountains National Park and Carlsbad Caverns National Park, southern Eddy County, just north of the New Mexico-Texas state border, far-southern New Mexico, USA.
