GEOMORPHOLOGY AND STRUCTURE OF THE WEST KAIBAB FAULT ZONE AND KAIBAB PLATEAU, ARIZONA

摘要

The western flank of the Kaibab Plateau contains three principal normal faults, all downthrown on the west, and locally developed monoclinal flexures. About half the total displacement of 2500 to 3000 feet between plateau summit and adjacent Kanab platform level is accomplished by these faults and monoclines, the other half by steady westward and northwestward regional dips. Strata on downthrown sides of major fault lines show downbending toward fault planes and indicate sagging of the edge of the lowered plateau blocks during faulting. Numerous minor faults, grabens, and swells affect the plateau arch. All deformational structures of the Kaibab region affecting Paleozoic and Mesozoic strata are regarded as Laramide in age, although positive stratigraphic evidence is completely lacking. The Kaibab plateau is dissected by numerous resequent and subsequent streams which follow the dip of the resistant, stripped Kaibab limestone or occupy fault lines. Scarps along faults are classified as resequent fault-line scarps, exposed by rapid stripping of weak Triassic shales from the plateau area. No evidence was found of peneplanation in a former erosion cycle. Small pediment remnants near the lower flanks of the plateau arch are interpreted as local features which do not require regional base-leveling. The Colorado River in the Kaibab region is explained as subsequent in origin. The ancestral river developed along a belt of weak Triassic shales which formerly encircled the southern end of the plunging Kaibab arch. Later intrenchment into resistant Paleozoic strata and removal of Mesozoic beds from the area have made the canyon appear to cut discordantly across the Kaibab arch.