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Research Paper GEOSPHERE Incision history of the Verde Valley region and implications for uplift of the Colorado Plateau (central Arizona) 1 2 2 GEOSPHERE; v. 14, no. 4 Richard F. Ott , Kelin X. Whipple , and Matthijs van Soest 1Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland 2School of Earth and Space Exploration, Arizona State University, 781 S. Terrace Road, Tempe, Arizona 85287, USA https://doi.org/10.1130/GES01640.1 12 figures; 3 tables; 1 supplemental file ABSTRACT et al., 2008; Moucha et al., 2009; Huntington et al., 2010; Liu and Gurnis, 2010; Flowers and Farley, 2012; Crow et al., 2014; Darling and Whipple, 2015; Karl- CORRESPONDENCE: richard .ott1900@ gmail .com The record of Tertiary landscape evolution preserved in Arizona’s transition strom et al., 2017). As part of this debate, the incision of the Mogollon Rim, zone presents an independent opportunity to constrain the timing of Colo­ the southwestern edge of the Colorado Plateau (Fig. 1), is not well constrained CITATION: Ott, R.F., Whipple, K.X., and van Soest, rado Plateau uplift and incision. We study this record of landscape evolution in the literature, and disparate ideas about its formation and incision history M., Incision history of the Verde Valley region and implications for uplift of the Colorado Plateau by mapping Tertiary sediments, volcanic deposits, and the erosional uncon­ have been proposed (Peirce et al., 1979; Lindberg, 1986; Elston and Young, ( central Ari zona): Geosphere, v. 14, no. 4, p. 1690– formity at their base, 40Ar/39Ar dating of basaltic lava flows in key locations, and 1991; Holm, 2001). The Cenozoic geomorphic evolution of the transition zone 1709, https:// doi .org /10 .1130 /GES01640.1. constructing geological cross sections along canyons to restore the paleorelief between the southwestern edge of the Colorado Plateau and the Basin and on the Tertiary erosional unconformity to test whether canyon incision requires Range Province (Fig. 2) is recorded by discontinuous sedimentary and volcanic Science Editor: Raymond M. Russo young (<10 Ma) Colorado Plateau uplift. Our cross sections and new 40Ar/39Ar deposits from this time interval. The goal of this study is to reveal the incision ages document that in the Verde Valley, relief across the ancestral Mogollon history of canyons cut into the southwestern margin of the Colorado Plateau, Received 27 November 2017 Revision received 6 April 2018 Rim that marks the southern edge of the Colorado Plateau was up to 1000 m in the upper Verde Valley. The timing and amount of incision of these canyons Accepted 4 May 2018 and averaged ~700 m in the Early­Middle Miocene, which is close to average constrain the uplift of the southwestern Colorado Plateau and thus are relevant Published online 5 July 2018 modern relief of ~800–1000 m. Although Middle­Late Miocene volcanics and to the debate over the timing of Grand Canyon incision and the role of rock sediments in places onlap the ancestral Mogollon Rim, suggesting an erosional uplift as a driver (Karlstrom et al., 2008; Flowers and Farley, 2012; Crow et al., origin, northeastward erosional retreat of an earlier tectonic escarpment is 2014; Young and Crow, 2014). Young (<10 Ma) uplift of the Colorado Plateau both plausi ble and consistent with displacement histories of the Grand Wash has been argued to be driving incision in the Grand Canyon, but the uplift fault to the NW and the Diamond Rim fault to the SE. Interestingly, the coin­ history of the Colorado Plateau and the timing of formation of different parts cidence of a rugged, sharply defined Mogollon Rim and a wide bench cut into of the Grand Canyon remain debated (Karlstrom et al., 2008; Liu and Gurnis, the Hermit shale below the escarpment today suggests that exposure of the 2010; Levander et al., 2011; Flowers and Farley, 2012; Karlstrom et al., 2014; Hermit shale may play an important role in cliff retreat and the morphological Darling and Whipple, 2015). The Verde Valley region with partially preserved expression of the Mogollon Rim in the Verde Valley region. Some modern can­ Cenozoic sediments and an extensive and well-preserved volcanic history yons cut into the retreating escarpment reflect re­excavation, deepening, and since Middle Miocene is a good location for constraining the incision history headward propagation of Miocene paleochannels largely buried by Middle­Late of the SW Colorado Plateau and therefore to test whether young uplift of the Miocene basalts. Despite evidence for similar total paleorelief, most canyons Colorado Plateau is required to explain the geology and dramatic local canyon show significant (~35%) deepening since 5 Ma with young incision decreasing incision. The aims of this study are to: (1) determine if there were multiple peri- OLD G to the SE. Incision rates during the period of active Miocene volcanism were ods of canyon cutting into the Mogollon Rim escarpment during the Cenozoic; below 20 m/m.y. but accelerated to 50–80 m/m.y. during the past 5–8 m.y. and (2) constrain the timing and amount of incision during each erosional event; were probably 100–160 m/m.y. during the Quaternary. The accelerated incision (3) determine whether deeply incised modern canyons require significant Late reflects base­level fall associated with breaching of the Verde Lake basin by Miocene to recent surface uplift of the SW Colorado Plateau; and (4) resolve OPEN ACCESS ca. 2.5 Ma and integration of the Verde River and thus does not require post– how the Mogollon Rim kept its sharp morphology despite the very low retreat Middle Miocene uplift of the southwestern edge of the Colorado Plateau. rate suggested by previous studies (Mayer, 1979; Ranney, 1988; Elston and Young, 1991) and how along-strike variations in escarpment morphology have INTRODUCTION been influenced by Quaternary base-level history. We build on previous studies that have used radiometric ages of lava flows The timing of surface uplift and canyon cutting on the Colorado Plateau has and provenance of Cenozoic sediments to constrain aspects of the history of This paper is published under the terms of the been vigorously debated for more than 100 years (e.g., Powell, 1875; Davis, landscape evolution in the central Arizona transition zone (e.g., Twenter, 1962; CC‑BY‑NC license. 1901; Blackwelder, 1934; McKee and McKee, 1972; Spencer, 1996; Karlstrom McKee and Anderson, 1971; McKee and McKee, 1972; Peirce et al., 1979; Ulrich © 2018 The Authors GEOSPHERE | Volume 14 | Number 4 Ott et al. | Incision history of Verde Valley region and implications for Colorado Plateau uplift Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/4/1690/4265559/1690.pdf 1690 by guest on 27 September 2021 Research Paper High: 3850 Low: 160 Sycamore Canyon Oak Creek Canyon K/Ar age < 6Ma 5 K/Ar age 6–12Ma 4 K/Ar age 12–20 Ma 6 8 Ar/Ar age < 6Ma Drake 13 9 Ar/Ar age 6–12Ma 8 2 6 Ar/Ar age 12–20Ma 19 Ar/Ar age > 20Ma Sedona 2Dry Beaver Creek Figure 1. Topography of the Verde Val­ 1 House Mountain ley with published K­Ar ages (triangles), 15 7 major drainages, and Ar/Ar ages from 17 3 Cottonwood 20 710 this study (circles). The color of the sym­ 16 bol indicates the radiometric age range. Wet Beaver Creek Canyon The shown K­Ar ages are documented in Black Hills 4 Table 1. Inset: Location of the Verde Valley 18 in the southwestern United States. 112°W 108°W 38°N Verde Valley West Clear Creek Canyon 1 Camp Verde 5 Las Vegas Grand Canyon 13 Colorado Plateau Flagsta Fossil Creek Canyon 9 34°N 3 Phoenix 12 11 and Bielski, 1983; Faulds, 1986; Elston and Young, 1991; House and Pearthree, flows are emplaced on different erosional surfaces and provide constraints 1993; House, 1994; Holm, 1998; Holm, 2001; Potochnik, 2001). Key events in on different episodes of incision and relief production. In addition, multiple this history include the formation of the Mogollon Rim, the timing of drain- cross sections were generated from existing maps supplemented by new field age reversal from northeastward flow from the Mogollon Highlands to gener- mapping to constrain the geometry and relief of the prevolcanic landscape in ally southern flow off the Colorado Plateau, and the incision of deep canyons the Verde Valley and to address how recent base-level history has influenced into the Plateau’s southwestern margin. Multiple erosional and aggradational the morphology of the study area and determine whether there is a record events have been described after the drainage reversal, but their timing is of post–Late Miocene Colorado Plateau uplift in this landscape. If all Colo- poorly constrained overall due to the scarcity of Cenozoic sediments, lack of rado Plateau uplift in the Verde Valley had occurred since the Late Miocene, detailed geologic maps, and shortage of radiometric ages in certain areas. we would expect little relief on erosion surfaces buried by mid-Miocene lavas Estimates for the timing of drainage reversal and subsequent canyon cutting (Fig. 3). On the other hand, mid-Miocene lavas burying significant paleotopog - vary synchronously with estimates of the formation age of the Mogollon Rim raphy at the edge of the Colorado Plateau would constrain the amount of pre– from Paleocene (Elston and Young, 1991) to Late Miocene–Pliocene (McKee mid-Miocene relief and uplift (Fig. 3). Our cross sections combined with radio- and McKee, 1972). metric dating, however, reveal that approximately two-thirds of the modern We present 15 Ar/Ar ages from nine lava flows selected to leverage and relief had formed before the emplacement of mid-Miocene basalts. The exca- complement published K-Ar dates, maps, and provenance data.

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