INCISED VALLEY FILLS OF THE MT. GARFIELD FORMATION, BOOK CLIFFS, GRAND JUNCTION, CO: FACIES ANALYSIS AND HETEROGENEITIES

Incised valley fills of the Late Cretaceous (Campanian) Mt. Garfield Formation, located in the eastern Book Cliffs escarpment near Grand Junction, Colorado are comprised of a variety of tidally influenced and continental facies. The Book Cliffs topography allows for exposure of the same incised valleys in numerous canyons aligned along depositional dip, which enables facies changes to be documented along dip. Accessible canyon exposures allows for detailed correlation at the parasequence scale, which delineates lateral and vertical complexities within the valley systems. Larger-scale geometries can be seen on continuous cliff escarpments between canyon exposures. Incised valley fill strata display significant lateral variability: some facies have limited extent and are restricted to individual canyon exposures, while other facies are correlated over a distance of kilometers and see in multiple canyons. Detailed facies analysis within the incised valley fill show at least seven distinct environments of deposition which occur repeatedly: tidally influenced channels, small deltaic successions, migrating tidal bars and burrowed siltstones interpreted as estuarine floor deposits, coals/mires, fluvial sandstones, and paleosols. One incised valley fill located in the distal shelf setting consists entirely of the deposits of migrating tidal bars. This particular valley is traceable to its interfluve surface expression.

Incised valley fill strata are multifaceted and unique features which complicate the stratigraphic interpretation of formations. Numerous incised valleys occur throughout the Mt. Garfield Formation and individual valleys are commonly nested and vertically stacked. Interpretations from previous studies at the member scale were combined with new data from this study and synthesized to yield an integrated high resolution sequence stratigraphic interpretation of the formation to provide a detailed framework to study the incised valley systems. This allows the total erosional relief of the nested incised valleys to be determined. The maximum relief noted of the nested incised valley fills can reach 45 meters.