Detrital-Zircon U-Pb Evidence Precludes Paleo–Colorado River Sediment in the Exposed Muddy Creek Formation of the Virgin River Depression
Total Page：16
File Type：pdf, Size：1020Kb
CRevolution 2: Origin and Evolution of the Colorado River System II themed issue Detrital-zircon U-Pb evidence precludes paleo–Colorado River sediment in the exposed Muddy Creek Formation of the Virgin River depression William R. Dickinson1, Karl E. Karlstrom2, Andrew D. Hanson3, George E. Gehrels1, Mark Pecha1, Steven M. Cather4, and David L. Kimbrough5 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA 2Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 97131, USA 3Department of Geoscience, University of Nevada–Las Vegas, Box 454010, Las Vegas, Nevada 89154-7003, USA 4New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA 5Department of Geological Sciences, San Diego State University, San Diego, California 92182, USA ABSTRACT course through the Grand Canyon to enter the For comparative purposes, previously unpub- Grand Wash Trough at the eastern end of mod- lished detrital-zircon data for the Chuska Sand- Only since 5–6 Ma has the Colorado River ern Lake Mead (Blair and Armstrong, 1979; stone are included in the Supplemental File1. fl owed through the western Grand Canyon House et al., 2005; Crossey et al., 2014). Vari- For visual comparisons of detrital-zircon into the Grand Wash Trough at the eastern ous lines of evidence (Lucchitta, 1989; Pelletier, populations, we use frequency plots of grain end of Lake Mead. Before then, the river may 2010; Dickinson, 2013; Lucchitta et al., 2013) ages, with analytical age uncertainties (±1σ) have fl owed through a paleocanyon transit- argue that a Miocene Colorado River transited for each grain age taken into account, normal- ing the Kaibab uplift at a stratigraphic level the Kaibab uplift through a paleocanyon near ized to subtend equal areas beneath each curve above the present eastern Grand Canyon the present site of the eastern Grand Canyon, of graphical displays. For statistical compari- to cross the Shivwits Plateau north of the but then crossed the Shivwits Plateau north of sons of detrital-zircon age populations and western Grand Canyon and enter the Virgin the western Grand Canyon to enter the paleo- subpopulations, we use Kolmogorov-Smirnoff River drainage, which exits the Colorado Pla- drainage of the Virgin River, from which it could (K-S) statistics to calculate the probability (P) teau into the Virgin River depression north then exit the Colorado Plateau into the Virgin that two age populations of grains, selected ran- of Lake Mead. U-Pb age spectra of detrital River depression (Bohannon et al., 1993) north domly from detrital-zircon concentrates, could zircons from Miocene–Pliocene basin fi ll of of Lake Mead (Fig. 1). In this paper, we evaluate have been derived from the same parent popula- the Muddy Creek Formation in the Virgin available U-Pb data (Forrester, 2009; Muntean, tion, and thereby assess the likelihood that two River depression preclude any paleo–Colo- 2012) from detrital zircons in Miocene–Pliocene detrital-zircon populations differ signifi cantly in rado River sand in Muddy Creek exposures strata of the Muddy Creek Formation, which age distribution. Where P ≥ 0.05, there is ≤95% but fail to show that a Miocene paleo–Colo- forms the basin fi ll of the Virgin River depres- probability (~2σ) that the two age populations rado River never fl owed into the Virgin River sion, to test for the presence of Colorado River could not have been derived by random selec- depression, because all exposed Muddy Creek sand in the local stratigraphic record. The age tion from a common parent population. Higher horizons sampled for detrital zircons post- spectra of the sampled detrital-zircon popula- P values denote progressively more age congru- date ca. 6 Ma. Detrital-zircon populations tions in exposed Muddy Creek strata refl ect ence of paired detrital-zircon populations. As from available surface collections cannot test exclusively Virgin River parentage with no dis- there is no current consensus whether the most for the presence of Colorado River sediment cernible component of admixed Colorado River appropriate P values derive from K-S analysis within unexposed lower Muddy Creek or sand, as Pederson (2008) concluded from petro- “with error,” including uncertainties in the con- sub–Muddy Creek strata in the subsurface graphic studies. We are unable, however, to test struction of the cumulative distribution function of the Virgin River depression. Alternate sce- fully for a Miocene infl uence of the Colorado (CDF), or “without error” in the CDF, we report narios include rejection of paleo–Colorado River on sediments of the Virgin River depres- P as calculated in both of the two alternate ways. fl ow into the Virgin River drainage at any sion because no sampled horizons of the Muddy time, or exit of the pre–6 Ma paleo–Colorado Creek Formation are older than ca. 6 Ma. First, VIRGIN RIVER DEPRESSION River from the upper Virgin paleodrainage we review the age and stratigraphy of the Muddy toward the northwest into the eastern Great Creek Formation in the Virgin River depression; The Virgin River depression is the deepest Basin without fl owing southwest into the Vir- next, we present the detrital-zircon evidence locus of crustal subsidence in the Lake Mead gin River depression through the Virgin River from Muddy Creek strata; then, we discuss the region west of the Grand Wash and Piedmont gorge, which may be younger than ca. 6 Ma. additional studies needed to assess the detrital- 1 INTRODUCTION zircon record for older Miocene strata within the Supplemental File. Excel fi le containing detrital- subsurface of the Virgin River depression; and, zircon data for the Chuska Sandstone. If you are viewing the PDF of this paper or reading it offl ine, Only since 5–6 Ma, after deposition of the fi nally, we discuss alternate scenarios for Colo- please visit http:// dx .doi .org /10 .1130 /GES01097 .S1 Hualapai Limestone, has the Colorado River rado River history not requiring any paleo–Colo- or the full-text article on www .gsapubs .org to view exited the Colorado Plateau along its present rado River fl ow into the Virgin River depression. the Supplemental File. Geosphere; December 2014; v. 10; no. 6; p. 1123–1138; doi:10.1130/GES01097.1; 11 fi gures; 2 tables; 1 supplemental fi le. Received 30 June 2014 ♦ Revision received 4 September 2014 ♦ Accepted 9 September 2014 ♦ Published online 12 November 2014 For permission to copy, contact [email protected] 1123 © 2014 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/6/1123/3334662/1123.pdf by guest on 28 September 2021 Dickinson et al. Ccc 114° W limit of Virgin ? KG 112° W E drainage R Eocene Claron CR Formation A KSW NV UT PVL F P SJR r SG F VR P W e H R V v Ka M i n R io UT 37° N in s 37° N g s ir re ? AZ V p ? b P e a d t b f i i l P Me a W C p K K u R V R r C Ko Mo e iv R F p TF al NV AZ W eo G -C Crooked OAB o o lo Ridge rad ra F lo d Co o CR1 River H er ( N = 5) LV Riv CR3 e as w Gr te e an rn 36° N G s d C 36° N Lake ra te yn CR2 C n rn R Mead d ? C fluvial y Bidahochi NV AZ n 806 - 7 M ? Fm MF F ( N = 2) H Little Colorado N 50 km MMF COL12 River V COL13 e DZ samples PS rd e towns and cities R W L Ki i limit of ve normal faults r F (barbells on Gila drainage downthrown sides) 114° W 112° W 806 - 6 Figure 1. Location of the Virgin River depression in relation to modern (blue—rivers and streams; brown—drain- age divides) and older (red—Miocene; green—Eocene adapted after Karlstrom et al., 2014) drainage patterns (MMF—Music Mountain Formation) inferred for the Grand Canyon region. The limit of the Virgin River depres- sion and of the associated Overton Arm Basin (OAB) is plotted to bound areas where pre-Cenozoic basement is ≥500 m below modern sea level (Langenheim et al., 2001). The northern limit of the Virgin River drainage is near Kanarraville gap (KG) east of the Pine Valley laccolith and latite (PVL). See Figure 8 for extensions of the Virgin River drainage basin north and west of the Caliente caldera complex (CCC) and the Kane Spring Wash caldera (KSW). Detrital-zircon (DZ) samples: (1) modern Colorado River in the Grand Canyon (Kimbrough et al., 2015): CR1—Kwagunt Rapids, CR2—Hance Rapids, CR3—Bass Rapids; (2) Little Colorado River (Kimbrough et al., 2015): 806–7 (Cameron), 806–6 (Winslow) off the map area to the southeast; (3) Eocene Music Mountain Forma- tion (Dickinson et al., 2012): COL12—Peach Springs Wash, COL13—Duff Brown Tank; (3) Miocene Crooked Ridge River (Lucchitta et al., 2011, 2013) on middle right (Hereford et al., 2015): fi ve samples not plotted indi- vidually; (4) fl uvial facies of the Miocene Bidahochi Formation (lower right): 806–12 and 806–13 of Kimbrough et al. (2015) from near Sanders off the map area to the southeast. See Figure 2 for detrital-zircon samples west of the Grand Wash fault. Selected faults: GWF—Grand Wash, HF—Hurricane, PF—Piedmont, TF—Toroweap. Selected streams: CR—Colorado River, ER—Escalante River, KC—Kanab Creek, MVW—Meadow Valley Wash, PR—Paria River, PW—Pahranagat Wash, SJR—San Juan River, VR—Virgin River. Selected towns and cities: A—Alamo, F—Flagstaff, Ka—Kanab, Ki—Kingman, Ko—Kaibito, L—Leupp, LV—Las Vegas, Me—Mesquite, Mo—Moapa, P—Page, PS—Peach Springs, SG—St.