STRATIGRAPHY AND GEOCHRONOLOGY OF TERTIARY DRAINAGE REVERSAL ACROSS THE TRANSITION ZONE, EAST-CENTRAL ARIZONA

On the southern Colorado Plateau boundary in eastern Arizona, Eocene northeast flowing streams beveled Paleozoic to Late Cretaceous northeast-tilted strata during the mid Eocene. A pulse of Late Eocene renewed Transition Zone uplift caused northeast-flowing streams to incise the Apache and Chediski paleocanyons west of Canyon Creek Fault. Mogollon Rim Fm fluvial clastics were deposited within the paleocanyons and on a broad alluvial plain to the northeast, 37.6-33.6 Ma. Subsequent tectonic subsidence and opposite-sense reactivation of faults in the Transition Zone caused deposition of the Whitetail Fm and volcanic flows in the Apache paleocanyon and on adjacent plateaus, 33.6 to 18.6 Ma, but did not stop northeastward stream flow. Emplacement of the 18.6 Ma Apache Leap Tuff ash flow sheet within the Apache paleocanyon terminated northeast flow onto the Colorado Plateau, initiating a period of ponding and drainage stagnation until 14.8 Ma emplacement of Black Mesa basalt flows. Drainage reversal to southwest stream flow on alluvial fans began locally on adjacent plateau uplands as early as 25.4 Ma. Reversal occurred locally within the Apache paleocanyon after 18.6 Ma but more profoundly after 14.8 Ma with deep incision of the ancestral Salt River paleovalley into Whitetail Fm sediments. This paleovalley was then filled with southwest distributed Dagger Canyon conglomerate concurrent with listric normal, half-graben rotational subsidence of the Tonto Basin after 9 Ma. The modern Salt River incised the Apache paleocanyon deposits slightly off-axis to the south prior to or during Pliocene eight degree northward flexure of the Apache paleocanyon. Thus, an ancestral Laramide paleocanyon provided a bedrock pathway for the modern Salt River following Late Miocene-Pliocene drainage reversal.