Geopic of the week: Deformation bands

Def Bands (18)b

The features that crisscross the surface of the sandstone pictured above are deformation bands.  They are micro faults that form where the bedrock is under strain.  They typically develop near larger faults and the orientation of the bands is determined by the orientation of the stresses acting on the rock.

The grains along deformation bands have been crushed, rotated, and reorganized.  The resultant bands are harder and less permeable than the rock they formed in, which causes them to stand in relief when the rock weathers.

Geologists look for deformation bands as indicators that a fault may be nearby.  This photo was taken in Van Buren County, Arkansas on the downthrown block of a normal fault.

For more views of deformation bands click here

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