The mechanics of graben development over deep-seated salt domes are described and illustrated by results of sectional-model experiments and study of the Heidelberg field, Mississippi. Relative vertical uplift of the salt produces graben structures in the overlying sediments. Within these structures downward movement of rock material occurs by wedge-shaped blocks. Fault movement at one boundary of a block is accompanied by similar movement along one or more fault planes at the opposing margin of the wedge. Increase of fault throw with depth and abnormally thick sections in graben blocks constitute effects impressed on the geometry of graben structures by deposition of sediments during deformation of the underlying strata.
The results of two sectional-model experiments originally recorded on motion-picture film are illustrated by eight photographs taken from individual frames. These experiments demonstrate the concentration of faulting in the upper beds over the crest of the salt uplift as deformation continues, relative age of faults, upward termination with consequent inactivity of the outer faults located at the margin of graben structures, and changes in fault dip as structural development proceeds.