A SEQUENCE STRATIGRAPHIC MODEL FOR THE REDWALL LIMESTONE IN THE GRAND CANYON, ARIZONA

The Redwall Limestone exposed in the Eastern and Central Grand Canyon of Arizona has similar facies and a similar sequence stratigraphic organization as the Leadville Limestone in Southwestern Colorado. The similarities in facies have been noted by previous workers (e.g. McKee and Gutschick, 1969; Kent and Rawson 1983), but here I offer an alternative sequence stratigraphic model.

The Grand Canyon Mississippian carbonates initiated slightly earlier (the Kinderhookian Whitmore Wash Member) than in Southwestern Colorado; both units are marked by basal conglomerates and are dominated by shallow water to supratidal facies. In southwestern Colorado, the Osagian Leadville Limestone thickens from highstand grain-dominated updip facies in the San Juan Mountains to westward prograding crinoidal shoal complexes which built out over deeper water, brozoan-rich cherty dolomitic wackestone and mudstone documented in core from the McElmo Dome Field, near Cortez Colorado. This progradation is indicated by an increase in bed and parasequence thickness and a progressive shift to more grain-supported lithologies (Klink et al., 2014). If this interpretation is applied to the facies of the Redwall Limestone in the Grand Canyon region, it suggest a similar progradational relationship for the crinoidal grain to packstone facies of the Mooney Falls member over the cherty bryozoan-rich deeper water facies of the Thunder Springs Member. Similar to the McElmo Dome cores in SW Colorado, exposures of this transition in the central Grand Canyon contain parasequences defined by alternations of these two facies which also appear to thicken, and contain more ooids up section. This progradational interpretation differs significantly from previous workers who view these two members as parts of two separate transgressive units. As the Redwall Limestone depositional system overfilled the margin, thinner, discontinuous shallow water parasequences of the Horseshoe Mesa Member where deposited. The final incised valley-filling Chesterian sequence of the Surprise Canyon Formation has not been recognized in Southwestern Colorado.