LARAMIDE-PALEOGENE GRAND CANYONE ORIGIN

There are five lines of evidence which suggest that much shaping and excavation of Grand Canyon occurred in Laramide-Paleogene time: (1) work by R.Young indicates significant Laramide-Paleogene channels were cut deeply through Paleozoic strata by NE-flowing streams in western Grand Canyon (GC) region, then backfilled-overtopped by a flood of south-derived fluvial gravels by 17 Ma, canyons later re-excavated; (2) the expansive Esplanade bench within western GC was beveled during lengthy base level control (not due to bedrock control) by a graded meanderbelt with W-flow, possibly coeval with an initial canyon cut through Kaibab Plateau, evidenced by (3) the anomalous large Nankoweap amphitheater of eastern GC, likely originating as a meanderbelt before/during Laramide Kaibab arch uplift, with N-ward flows along N-S Laramide high-angle faults, like in western GC. Following regional drainage reversal a new Colorado River incised the Marble Gorge southward as a linear canyon east of Nankoweap-Chuar Buttes, joining the relict gorge across Kaibab arch and isolating the old meanderbelt; (4) The resistant eastern lip of the inactive eastern GC gorge at 1830 m elev. likely served as stable knickpoint-base level for extensive westward-prograded deposition of Bidahochi-Richville-Quemado Fms in Little Colorado River Valley (LCRV), derived from San Juan Mts-Mogollon-Datil regions, after 16 Ma. Before ~5 Ma, ancestral squawfish fossils indicate some Colorado River-LCRV aquatic connection, but any former pre-6 Ma riverine exit off Colorado Plateau (CP) is problematic - a significant westward paleo-drainway with gravel remnants crosses Telegraph Flat-Kanab region below 1750 m elev. (Van Williams). Waters of a shallow sediment-filled LCRV ('Hopi Lake') eventually overtopped the eastern GC gorge lip (with rare sediment evidence) at 6 Ma, initiating new downcutting of Marble and LCR gorges, and cleaning out the clogged GC; (5) A Paleogene GC gorge may solve the magnitude/timing problem of Dutton's (1882) great denudation (>one km removed since ~early Oligocene from across the CP) by serving as a late Paleogene exit path before western GC became clogged (is this the origin of Esplanade surface?) - the alternate 'strike valley' hypothesis of post-6 Ma entire CP denudation and cutting of GC is unreas onably fast.