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.
