Late Cenozoic Tectonics of Northern and Western Imperial Basin

Thomas W. Dibblee, Jr.

The Imperial basin, or Salton trough, is filled with as much as 5 km of middle(?) and late Cenozoic clastic sedimentary deposits. They are buried by alluvium under the major part of this basin but are exposed along the northern margin and more extensively on the west side. In both of these areas, the sedimentary fill is on an irregular basement surface and buttresses out northeastward and westward against the pre-Tertiary basement terranes elevated in the adjacent mountain ranges. Unconformities within the sedimentary fill record recurrent movements during deposition.

The San Andreas fault zone along the northeastern margin of this basin dies out on the surface east of Salton Sea. Along this fault zone, the sedimentary fill is wrinkled into numerous small folds by right lateral drag movements as this fault dies out southeastward. This fault may step southward as several faults, including the active Imperial fault, into the basin center.

Where the thick sedimentary fill buttresses westward against the basement terrane of the northern Peninsular Range province, the fill is severely deformed by right lateral slip and uplift on faults of the San Jacinto and Elsinor fault zones that converge southeastward into the basin. On these faults, deformation of the sedimentary fill is generally similar to that on the San Andreas fault zone but complicated by uplift and left-slip on subsidiary transverse faults. The general trend of fold axes throughout this region is east-west with variations of as much as 30° either way.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.