Detrital Sanidine 40Ar/39Ar Dating Confirms
Total Page：16
File Type：pdf, Size：1020Kb
Research Paper THEMED ISSUE: CRevolution 2: Origin and Evolution of the Colorado River System II GEOSPHERE Detrital sanidine 40Ar/39Ar dating confirms <2 Ma age of Crooked 1 of 17 Ridge paleoriver and subsequent deep denudation of the / GEOSPHERE, v. 17, no. X southwestern Colorado Plateau https://doi.org/10.1130/GES02319.1 Matthew T. Heizler1, Karl E. Karlstrom2, Micael Albonico2, Richard Hereford3, L. Sue Beard3, Steven M. Cather1, Laurie J. Crossey2, 12 figures; 2 tables; 1 set of supplemental files and Kurt E. Sundell4 1New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801, USA 1st pages 2 CORRESPONDENCE: [email protected] University of New Mexico, 221 Yale Boulevard NE, Albuquerque, New Mexico 87106, USA 3U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, Arizona 86001, USA 4 CITATION: Heizler, M.T., Karlstrom, K.E., Albonico, M., University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA Hereford, R., Beard, L.S., Cather, S.M., Crossey, L.J., and Sundell, K.E., 2021, Detrital sanidine 40Ar/39Ar dat- ing confirms <2 Ma age of Crooked Ridge paleoriver ABSTRACT ■ INTRODUCTION and subsequent deep denudation of the southwestern Colorado Plateau: Geosphere, v. 17, no. X, p. 1– 17, https://doi.org/10.1130/GES02319.1. Crooked Ridge and White Mesa in northeastern Arizona (southwestern United States) preserve, as Reconstructing the age and evolution of paleo- inverted topography, a 57-km-long abandoned alluvial system near the present drainage divide between landscapes in the Colorado Plateau–Grand Canyon Science Editor: Andrea Hampel the Colorado, San Juan, and Little Colorado Rivers. The pathway of this paleoriver, flowing southwest region (southwestern United States) continues to Associate Editor: Christopher J. Spencer toward eastern Grand Canyon, has led to provocative alternative models for its potential importance in provide stimulating debate that can foster devel- Heizler_GES02319 carving Grand Canyon. The ~50-m-thick White Mesa alluvium is the only datable record of this paleoriver opment of improved dating and landscape models. Received 15 July 2020 40 39 Revision received 11 September 2020 system. We present new Ar/ Ar sanidine dating that confirms a ca. 2 Ma maximum depositional age For decades, geologists have speculated about Accepted 15 January 2021 for White Mesa alluvium, supported by a large mode (n = 42) of dates from 2.06 to 1.76 Ma. Older grain possible evolution of paleoriver pathways and modes show abundant 37–23 Ma grains mostly derived ultimately from the San Juan Mountains, as have debated “old” (ca. 70 Ma), “intermediate” is also documented by rare volcanic and basement pebbles in the White Mesa alluvium. A tuff with (ca. 25 Ma), and “young” (post–10 Ma) models to an age of 1.07 ± 0.05 Ma is inset below, and hence provides a younger age bracket for the White Mesa explain the modern iconic landscape of the Grand alluvium. Newly dated remnant deposits on Black Mesa contain similar 37–23 Ma grains and exotic Canyon region (e.g., Karlstrom et al., 2012a). Pre- pebbles, plus a large mode (n = 71) of 9.052 ± 0.003 Ma sanidine. These deposits could be part of the served paleoriver deposits are relatively scarce due White Mesa alluvium without any Pleistocene grains, but new detrital sanidine data from the upper to deep erosion of the Colorado Plateau region, yet Bidahochi Formation near Ganado, Arizona, have similar maximum depositional ages of 11.0–6.1 Ma these remnants provide some of the most import- and show similar 40–20 Ma San Juan Mountains–derived sanidine. Thus, we tentatively interpret the ant data sets for reconstructing landscape evolution <9 Ma Black Mesa deposit to be a remnant of an 11–6 Ma Bidahochi alluvial system derived from the to the extent their ages and pathways are known. now-eroded southwestern fringe of the San Juan Mountains. This alluvial fringe is the probable source Gravels of Crooked Ridge and White Mesa area for reworking of 40–20 Ma detrital sanidine and exotic clasts into Oligocene Chuska Sandstone, Mio- (northeastern Arizona) have been part of models cene Bidahochi Formation, and ultimately into the <2 Ma White Mesa alluvium. The <2 Ma age of the for the evolution of the Colorado River system and White Mesa alluvium does not support models that the Crooked Ridge paleoriver originated as a late carving of Grand Canyon for many decades. Various Oligocene to Miocene San Juan River that ultimately carved across the Kaibab uplift. Instead, we inter- workers have envisioned that an Oligocene–early pret the Crooked Ridge paleoriver as a 1.9–1.1 Ma tributary to the Little Colorado River, analogous to Miocene river flowed southwest from Utah into Ari- modern-day Moenkopi Wash. We reject the “young sediment in old paleovalley” hypothesis based on zona along the Crooked Ridge pathway (Babenroth mapping, stratigraphic, and geomorphic constraints. Deep exhumation and beheading by tributaries of and Strahler, 1945; Strahler, 1948; Cooley and David- the San Juan and Colorado Rivers caused the Crooked Ridge paleotributary to be abandoned between son, 1963; McKee et al., 1967; Hunt, 1969; Lucchitta 1.9 and 1.1 Ma. Thermochronologic data also provide no evidence for, and pose substantial difficulties et al., 2011, 2013). The models differ regarding how with, the hypothesis for an earlier (Oligocene– Miocene) Colorado–San Juan paleoriver system that and when such a Colorado–San Juan paleoriver got flowed along the Crooked Ridge pathway and carved across the Kaibab uplift. integrated across the Kaibab uplift to carve Grand This paper is published under the terms of the Canyon. The alignment of the Crooked Ridge depos- CC-BY-NC license. Matthew Heizler https://orcid.org/0000-0002-3911-4932 its with a 2.5-km-wide break in the Echo Cliffs called © 2021 The Authors GEOSPHERE | Volume 17 | Number X Heizler et al. | 2 Ma Crooked Ridge paleoriver 1 Research Paper “The Gap” and with the segment of eastern Grand Juan paleoriver. All of these workers considered Hereford et al. (2016) mapped and character- Canyon that cuts across the Kaibab uplift (Fig. 1) the deposits on White Mesa and Crooked Ridge to ized the 50-m-thick succession of gravel, sand, and make the Crooked Ridge deposits a potential can- be the same map unit. silt and called it the White Mesa alluvium. They didate for the remains of a major paleoriver. Lucchitta et al. (2011, 2013) reinvigorated dis- reported four <2 Ma detrital sanidine grains in 2 of 17 The deposits were mapped by Cooley and cussion of these deposits and named the “Crooked the White Mesa alluvium, an unexpectedly young / Davidson (1963, their figure 10) as the “gravel on Ridge River”. We choose the term “Crooked Ridge age. By applying the surface mapping of Cooley White Mesa” and interpreted as a late Miocene paleoriver” because there is no current Crooked et al. (1969) with other known incision rates and and Pliocene ancestral Colorado River–San Juan Ridge river. They characterized the pebble and cob- ash dates on surfaces of different landscape posi- River system. Cooley et al. (1969, their plate 1) ble types in the alluvium and made the argument tion, these authors proposed that the White Mesa showed the name “Crooked Ridge” for a ridge of (as did Hunt [1969] p. 106) that “exotic” clasts of alluvium is <2 Ma and was deposited by a former the outcropping gravels. Hunt (1969, his figures volcanic and basement lithologies came from the tributary to the Little Colorado River rather than a 1st pages 68, 69) called these sediments the “Tertiary gravel San Juan Mountains located to the northeast, and major trunk river. Karlstrom et al. (2017) suggested of Kaibito Plateau” and also interpreted them to that these are deposits of a major river, the San that its landscape position records a denudation have been deposited by a pre–late Miocene San Juan paleoriver. history for the region consistent with rapid incision 112°W 111°W 110°W 109°W ID Henry Explanation WY Mountains 38°N River incision point White Mesa alluvium (ca. 2Ma) UT Colorado Heizler_GES02319 NV Plateau CO o Detrital sanidine Bidahochi Fm. undivided (6-9 Ma) d Thermochronology a r Base, lacustrine Bidahochi Fm. (14-16 Ma) Figure 1. Crooked Ridge paleoriver re- r e o v S l i gion (northeastern Arizona, United CA AZ NM t r o C R States) and dated detrital sanidine a i g h t Bullfrog sample locations. Red line shows the C Marina S a n western part of the Crooked Ridge l Mexican J u i s POW-14 Bluff R i a paleoriver pathway of Lucchitta et al. Hat v e n r (2013) and corresponds to the profile SJR-2 in Figure 10. Fluvial upper Bidahochi POW-7A Formation undivided is in orange with GLGC-T N a v a j o M t n UT CO N 37°N newly dated samples on Black Mesa and POW-18 a AZ NM near Ganado, Arizona. The base of ca. v a j Lees o C r e S k e l e t o C 16 Ma lacustrine Bidahochi Formation Ferry e k n h Carizzo K M e s a i is shown with a yellow line. Thermo- o n hite n a M o r m W Mtns l chronology samples show that rocks i g e s Mesa Lava Creek B WM i d e b R along the modern San Juan and Col- a WM-2 WMZ-NUP W b d CK-3 orado Rivers were beneath 1–2 km of PR-AZ-5 k e a o u r o e PR-AZ-3 s Mesozoic strata until after 6 Ma (Hoff- C g h p d B l a PR-AZ-4 R i BM-1 c k C man, 2009; Karlstrom et al., 2014).