Detrital-Zircon U-Pb Evidence Precludes Paleo–Colorado River Sediment in the Exposed Muddy Creek Formation of the Virgin River Depression

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

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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—drainage 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 depression 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 individually; (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. George, W—Williams. States (dot-dash boundaries): AZ— Arizona, NV—Nevada, UT—Utah.

faults marking the edge of the high-standing between parallel strands of the sinistral Lake lobes, respectively, of the Virgin River depres- Colorado Plateau transected by the Grand Can- Mead fault system (Fig. 2) is adjacent on the sion (Fig. 2). yon (Fig. 2). Within the 1250 km2 depression, south and contiguous with the Virgin River The Mormon and Mesquite Basins of the Cenozoic basin ﬁ ll extends to depths ≥500 m depression. Precambrian basement below a Virgin River depression are each buried half below sea level (Fig. 3), and it is thicker than thick Paleozoic–Mesozoic succession lies at grabens, bounded on the east by normal faults elsewhere in the Lake Mead region, except depths of 3000–6000 m below sea level in the (Bohannon et al., 1993). Subsurface strata are within the Overton Arm pull-apart basin (Cam- structural keels of the Mesquite and Mormon inclined eastward into the bounding faults, but pagna and Aydin, 1994). The latter depocenter Basins, occupying the eastern and western fanning dips in Cenozoic strata of both basins

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Figure 2. Pre-Quaternary geo- P Tertiary Mormon M t n s gravel P logic map of the Lake Mead V volcanics M plains region (cross-hatched area of 10 km P M Mesozoic P White Basin is discussed in North F9 P UT the text) showing the locations P Paleozoic X Mesquite of key detrital-zircon samples basin AZ X Precambrian F11 & F18 (N = 2) PF from (1) the Miocene–Plio- P cene Muddy Creek Forma- Table 114° 30′ W P Mesa To n tion (solid squares) including i o V20R basin s s three Forrester (2009) samples r e M e p ver from the Mesquite Basin at P d Ri M F36 X V Ty V Mesquite Flat Top Mesa (F36) and Bea- W P r v e in Ty i irg ver Dam Wash (F11, F18), and To R V e NV AZ nine Muntean (2012) samples g i n n r g including four from the Mor- a V i Mormon R 806-10 M Moapa basin M mon Basin (M1–M4) and ﬁ ve n To PW P yo n F from the Overton Arm Basin i C X P n s C a a Mobil (OAB; M5, M8–M9, M11– C b P Virgin M X M12) within 1 km to 5 km w e To l 1A o R F r a P M r of Overton Arm (the latter d W A n V P e M1-M4 Ty G are not plotted for reasons of l G (N=4) scale); (2) post–Muddy Creek X M B 36° 30′ N A 36° 30′ N Pliocene–Pleisto cene terrace WF M13 O P Ty C F To deposits (open squares) inset R (N = 5) B M into incised Muddy Creek P P P Formation of the Virgin River m r M F A P depression (F9 of Forrester, P S F R To LR W 2009; M13 of Muntean, 2012); To To G M X NV AZ To (3) Miocene–Pliocene (LMSP2, Ty P H5HW) deposits (solid cir- P White F cles) of the Colorado River To n BF R Basin o F X G W BS t To To r (Kimbrough et al., 2015); and M M V e (4) modern sand (open circles) v M X P of the Virgin River (VR20 of O GWF P BF To To Forrester, 2009; 806–10 of V H To P Kimbrough et al., 2015). Map LMSP2 P Tertiary Virgin Basin was compiled from Ander- L Successions M (Quaternary son and Beard (2010), Beard Boulder F alluvium Basin C omitted) et al. (2007, 2010), Blair and H5HW R V To V Armstrong (1979), Bohan- P To Ty non (1983, 1984), Campagna 36° N V 36° N To post-Hualapai and Aydin (1994), Felger and W Beard (2010), Forrester (2009), CR D To V To Hualapai House et al. (2005), Howard V X Limestone F P et al. (2010), Muntean (2012), To C F V L Schmidt et al. (1996), Swaney X W To F G To SS X et al. (2010), Umhoefer et al. X X pre-Hualapai (2010), and Wallace et al. H X W (2005). Faults (half-arrows To V 114° 30′ W denote relative motions on Lake Mead strike-slip faults, barbells denote downthrown blocks at normal faults): BRF—Bitter Ridge, BSF—Bitter Spring Valley, CCF—Cabin Canyon, CWF—California Wash, GBF—Gold Butte, GWF—Grand Wash, HBF—Hamblin Bay, LCF—Lost Cabin Range, LMF—Lakeside Mine, LRF—Lime Ridge, PF—Piedmont, RSF—Rogers Spring, SSF—Salt Spring Wash, WRF—Wheeler Ridge. Selected streams: CR—Colorado River (above and below Lake Mead), DW—Detrital Wash, GW—Grand Wash, HW—Hualapai Wash, MR—Muddy River, MVW—Meadow Valley Wash. Circled dots denote the towns of Mesquite in the Virgin River depression and Moapa in the Glendale Basin.

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depth thickness instead the local expression of the “red sand- scale (m) (m) s t r a t i g r a p h i c u n i t (s) (250) (detrital zircons) stone unit” of Bohannon (1984) that underlies Figure 3. Geologic units M u d d y C r e e k F o r m a t i o n the Muddy Creek Formation in the Mormon 885 (4–10 Ma) Basin to the east (Fig. 3). In either case, the (Bohannon et al., 1993) pene- 500 m trated by the Mobil Virgin (215) (gypsiferous beds) thickness of Muddy Creek Formation in the River 1A test well (Fig. 2) in 1000 Glendale Basin is much less (<50% to <5%) 640 “r e d s a n d s t o n e u n i t” the Mormon Basin of the Vir- (12–10 Ma) than in the Virgin River depression. gin River depression. Anno- H o r s e S p r i n g F o r m a t i o n 520 Muddy Creek Formation Age tated ages of pre–Muddy Creek (24–12 Ma) 2000 Cenozoic units are projected Tertiary into the well bore from areas Basalt that is interbedded within the upper- 1335 M e s o z o i c s t r a t a outside the Mormon Basin most Muddy Creek Formation in exposures near using data from Harlan et al. Mesquite (Fig. 2) in the Mesquite Basin has (1998), Castor et al. (2000), 4000 yielded a whole-rock K-Ar age of 4.1 ± 0.2 Ma

pre-Tertiary (Williams, 1996), which is Zanclean (Lower Beard et al. (2007), and Ander- 2440 P a l e o z o i c s t r a t a son and Beard (2010). Pliocene) according to Hilgen et al. (2012) and Walker et al. (2013), and which provides close 1000 m P r e c a m b r i a n b a s e m e n t age control for the top of the Muddy Creek For- 6000 mation in the Virgin River depression (Fig. 4). A younger tuff, ca. 3 Ma in age, intercalated within Muddy Creek Formation of the Glendale Basin imply that structural relief was developed dur- The Muddy Creek Formation of the Mes- (HH of Fig. 4) implies that Muddy Creek depo- ing basin fi lling over the past ~25 m.y., with quite Basin is composed dominantly of fi ne- to sition continued longer in the Glendale Basin net crustal extension estimated at 64% ± 8% medium-grained fl uvial sandstone with subor- before the latter was incorporated into the Virgin from stratal reconstructions based on seismic dinate intercalated conglomerate and siltstone, River drainage. An older horizon of the Muddy stratigraphy (Bohannon et al., 1993; Langen- some of which is lacustrine (Billingsley, 1995; Creek Formation in the Mesquite Basin has heim et al., 2001). Locally exposed angular Williams, 1996; Williams et al., 1997; Forrester, yielded a Miocene mammalian fauna (Williams unconformities within the basin fi ll are inter- 2009). The lacustrine beds, in part gypsiferous, et al., 1997) of the Hemphillian North American preted as the record of deformation associated are more abundant southward in the Mormon Land Mammal Age (NALMA), which began with syndepositional tectonism (Muntean, Basin and into the Overton Arm Basin, but as early as ca. 9 Ma (Woodburne and Swisher, 2012). A buried interbasinal sill that formed these beds are subordinate in surface outcrops 1995; Hilgen et al., 2012) but lasted until 4.9 Ma along the upthrown side of the buried normal (Muntean, 2012). Logical options for delivery (Hilgen et al., 2012) or even 4.8–4.7 Ma (Flynn fault separating the Mormon and Mesquite of sandy Muddy Creek detritus to the Virgin et al., 2005). Basins reaches to within 1500 m of the sur- River depression and the associated Overton Dated basalt interbedded within the lowest face of basin fi ll in the Virgin River depression. Arm Basin include the ancestral Virgin River, informally named member of exposed Muddy The Glendale Basin west of the Virgin River a paleo–Colorado River that had entered the Creek Formation (Muntean, 2012) in outcrops depression (Fig. 2) is a much shallower half ancestral Virgin River drainage basin, and tribu- west of Overton Arm in the Overton Arm Basin graben containing ≤500 m of Cenozoic basin taries to the ancestral Virgin River that tapped (Fig. 2) provides age control for the oldest fi ll (Langenheim et al., 2001). igneous sources associated with Tertiary cal- exposed Muddy Creek Formation. A whole- deras north of the Virgin River depression rock K-Ar age of 8 Ma (with no ± uncertainty Muddy Creek Formation Stratigraphy (Peder son, 2008). cited), was reported for an Overton Arm basalt The Muddy Creek Formation of the Glen- by Eberly and Stanley (1978) in a paper focused Apart from narrow bands of Quaternary sedi- dale Basin (Fig. 2), west of the Virgin River on Cenozoic basins of southwestern Arizona, ment along the Virgin River and its tributaries, depression, is dominantly lacustrine claystone, but their age for the basalt is older than younger the youngest strata within the Virgin River deposited in “Muddy Creek lake” (Schmidt isotopic ages for Overton Arm basalts from depression form the Miocene–Pliocene Muddy et al., 1996) as upper green claystone, 5–30 m more recent geochronology, and it is discounted Creek Formation. This unit extends across the thick, and lower red claystone, of which only here as an unreliable age control for exposed full extent of the Mormon and Mesquite Basins, 45 m are exposed, but which reaches total thick- Muddy Creek Formation. except for isolated outcrops of older Cenozoic nesses of 350–380 m where penetrated in water Feuerbach et al. (1991) obtained a K-Ar age strata along the structurally shallow western wells. Fluvial terrace gravels overlying lacus- of 6.02 ± 0.39 Ma (their sample 6) for a plagio- fl ank of the Mormon Basin (Fig. 2) and Plio- trine claystones of the Glendale Basin were clase concentrate from an Overton Arm basalt, cene–Pleistocene terraces inset into Muddy deposited during dissection of the lakebeds after and Beard et al. (2007) reported preliminary Creek basin fi ll (Forrester, 2009). The full thick- integration of the local watershed into the Virgin 40Ar/39Ar isochrons of 6.15 Ma and 6.60 Ma for ness (885 m) of the Muddy Creek Formation River fl uvial system of the Virgin River depres- the same basalt fl ow. Felsic tephra in the Muddy was penetrated by the Mobil Virgin River 1A sion by breaching of a low divide between the Creek Formation exposed not far below the test well near the center of the Mormon Basin Glendale and Mormon Basins after deposition Overton Arm basalts correlates well geochemi- (Figs. 2–3), but only the uppermost 250 ± 50 m of the Muddy Creek Formation. There is uncer- cally with the Blacktail Creek ash (Muntean, section of the Muddy Creek Formation (<30% tainty (Schmidt et al., 1996) whether the lower 2012), and another tephra layer in the same gen- of its total thickness) is exposed in the Virgin red claystone of the Glendale Basin is properly eral stratigraphic position has been correlated River depression (Forrester, 2009). assigned to the Muddy Creek Formation, or is with the Walcott ash (Beard et al., 2007). The

1126 Geosphere, December 2014

Muddy Creek Formation Eastern Lake Mead Basins All other available detrital-zircon samples from Glendale Virgin River Temple Gregg Grand Wash the Muddy Creek Formation (see following dis- Ma Ma and Table depression basin basin trough cussion) are from overlying horizons younger 2 Mesa basins and 2 Overton than 6 Ma in age. Arm Given that the ~250 m of Muddy Creek For- HH (14) basin mation exposed in the Virgin River depression Sandy were deposited largely, if not entirely, dur- Point 4 4 wb (20) ing the interval between 6.6–6.0 Ma and ca. 4 b (8) Ma, the implied net rate of sedimentation was marl (15) t) b (11) 110 ± 15 m/m.y. during latest Miocene and

WC (14) earliest Pliocene time. If that sedimentation

pai offse

fault system 6 t (12) pb (9) t (16) 6 rate is projected backward in time for deposi-

i WA (2) ) tion of the unexposed ~635 m of lower Muddy

Platea

BC (13) r

m Huala

stone

O Creek Formation penetrated by the Mobil Vir-

ite Hills)

t (12) T

[~1

tuff Hualapa gin River 1A test well in the subsurface of the

(275

Lime t (8) -Wh Mormon Basin (Fig. 3), then the indicated age

unexposed ]

8 of Colora

tem 8

[~265 M]

irgin IMES of the base of the Muddy Creek Formation is ca.

L Muddy Creek t (4) b (11) hV t (3) 12 Ma. That projected basal age for the Muddy

[~240 m

fault sys

estone

AI t (2) est edge Creek Formation is almost certainly too old, for

b (11) (Sout

)

Formation w the underlying “red sandstone unit” of Bohan-

10 b (1) Ridge 10 non (1984) has yielded multiple isotopic ages

along “red ALAP

pb (9) al., 2007

alapai Lim

ide Mine t (4) eler (N = 8) of 11.9–10.05 Ma (Harlan et al., 1998;

HU sandstone Hu t (2) t (8) Castor et al., 2000; Beard et al., 2007) where

wb (18) unit” -Lakes exposed within and near White Basin (Fig. 2),

Beard et t (5,9) Wash fau

ge - Whe t (2) b (11) h t (6) 12 s 12 ~40 km south-southwest of the test well. The

Ran t (11) b (11) Wa Arm” ( lowest 215 m section of Muddy Creek Forma- w=wholerock Grand

84) n t (19)

ring abin t (2) tion in the test well is reported as gypsiferous K-Ar p = plagioclase t (11) t (19) t (8) ages b = basalt (Fig. 3), suggestive of playa deposition within t (4) t=tuff Lost C Salt Sp an undrained depression. The base of overlying

of Overto

rand Was 14 t (11) t (2) annon, 19 14 Ar/Ar ages: b = basalt t (4) t (17) nongypsiferous Muddy Creek Formation in the t = felsic tuff b (11) (Boh

“rocks well is calculated to be ca. 10 Ma using a sedi- fossil assemblage b (7)

gh” t (11) t (8) ocks of G mentation rate of 110 m/m.y. for the formation, tephrachronology t (7) t (19) “r HH - Upper Horse Hill trou and that date can perhaps be taken as a maxi- 16 16 WC - Wolverine Creek mum age for the base of fl uvial Muddy Creek WA - Walcott ash Formation in the Virgin depression. A basal age BC - Blacktail Creek of 10 Ma for fl uvial Muddy Creek Formation pre - Hualapai Hualapai Ls. post - Hualapai matches the youngest known isotopic age for the “red sandstone unit” and also the estimate Figure 4. Isotopic and fossil ages for late Neogene (<16 Ma) stratigraphic units in sedi- of Beard et al. (2007) for initiation of Muddy mentary basins of the Lake Mead region including the Virgin River depression (Fig. 2). Creek sedimentation. Age uncertainties <1 Ma are not plotted, some closely spaced ages are combined, and some redundant ages are omitted. Ages for the “red sandstone unit” of Bohannon (1984) within Lake Hualapai Extent and near White Basin (Fig. 2) are identifi ed from correlations by Beard et al. (2007). Sources of data (numbers in parentheses): 1—Anderson et al. (1994), 2—Beard et al. (2007), 3—Blair There is widespread agreement (Lucchitta, (1978), 4—Blythe et al. (2010), 5—Castor et al. (2000), 6—Crossey et al. (2014), 7—Dueben- 1989; Faulds et al., 2001a, 2001b; House et al., dorfer and Sharp (1998), 8—Faulds et al. (2001a), 9—Feuerbach et al. (1991), 10—Harlan 2005, 2008; Spencer et al., 2001, 2008b) that the et al. (1998), 11—Howard et al. (2010), 12—Metcalf (1982), 13—Muntean (2012), 14—Peder- course of the Colorado River was not integrated son et al. (2001), 15—Schmidt et al. (1996), 16—Spencer et al. (2001), 17—Swaney et al. through the western Grand Canyon (Fig. 1) into (2010), 18—Theodore et al. (1987), 19—Umhoefer et al. (2010), 20—Williams (1996). the Grand Wash Trough at the eastern end of Lake Mead until after deposition of the lacustrine Hualapai Limestone, which extends east- two ashes have been dated to 6.62 ± 0.003 Ma Creek Formation are thus coeval with upper- ward to the Grand Wash Cliffs at the mouth and 6.27 ± 0.04 Ma, respectively (Morgan and most Hualapai Limestone (Crossey et al., 2014) of the modern Grand Canyon. All preserved McIntosh, 2005). exposed near Lake Mead 50–65 km to the south, exposures of the Hualapai Limestone (Fig. 2) We accordingly infer that exposed Muddy near the mouth of the modern Grand Canyon are restricted to a belt, 42.5 km (east-west) Creek horizons of the Overton Arm Basin and (Fig. 4). A detrital-zircon sample collected from by 17.5 km (north-south), in the Grand Wash the Virgin River depression are no older than strata interbedded with 6.6–6.0 Ma basalts near Trough and the downfaulted Gregg and Temple 6.6–6.0 Ma, in latest Miocene (Messinian) Overton Arm (Fig. 4) yielded only seven zircon Basins to the west (Fig. 4). House et al. (2008) time (Hilgen et al., 2012; Walker et al., 2013). grains that do not cluster in age and are too few suggested that the original extent of Lake Huala- The oldest exposed horizons of the Muddy for rigorous analysis of their age distribution. pai can be reconstructed by projecting a paleo-

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shoreline at the elevation of the top of exposed pai Limestone. Gypsiferous lacustrine strata in the two age subpopulations is not separable with Hualapai Limestone across modern topography, the lower Muddy Creek Formation penetrated confi dence from comparable age populations in thereby inferring that Lake Hualapai fi lled the by the Mobil Virgin River 1A test well in the either modern or Pliocene Colorado River or Virgin River depression and spilled into the Mormon Basin may be correlative with lower Virgin River sands, nor from upstream sands of Glendale Basin farther west. The most favored horizons of the Hualapai Limestone but are modern or Miocene Colorado River tributaries. elevation for the reconstructed paleoshoreline is lithologically dissimilar and now lie near sea Kolmogorov-Smirnoff analysis (Table 1) shows 720 m (Spencer et al., 2008b, 2013), the eleva- level more than 600 m below the elevation of that pre–75 Ma Muddy Creek sands are largely tion at the top of Hualapai Limestone in the the lowest exposed Hualapai Limestone. congruent with both Virgin-related and Colo- White Hills of Temple Basin to the south of the The oldest known Hualapai Limestone rado-related sands, there being <95% confi - Virgin Basin of Lake Mead (Fig. 2). To accom- (ca. 12 Ma) occupies the fl oor of Grand Wash dence (P ≥ 0.05) that most sample subsets could modate exposures of Hualapai Limestone that Trough at the foot of the escarpment marking the not have been derived from the same parent reach elevations in excess of 900 m on Grape- edge of the Colorado Plateau, and the top of the population. The exceptions are sands from the vine Mesa in the Grand Wash Trough (Wallace Huala pai Limestone is estimated to be ca. 6 Ma modern Little Colorado River and the Miocene et al., 2005), an eastern arm of Lake Hualapai from exposures in the White Hills of Temple Bidahochi Formation upstream to the southeast is conventionally added to the lake (Roskowski Basin, ~35 km to the west (Fig. 4). The base of from the Grand Canyon. Those two sample sub- et al., 2010; Dickinson, 2013), or else a separate Hualapai Limestone is clearly time-transgres- sets are themselves mutually congruent (P = “Lake Grand Wash” is postulated with a sur- sive, onlapping its substratum westward from 0.48/0.33), but their incongruence with other face elevation of 912 m within the Grand Wash the Grand Wash Trough to the Temple Basin Colorado-related sands shows that detritus of Trough (Spencer et al., 2013). The latter pos- (Fig. 4). The “rocks of Overton Arm” (Beard Little Colorado River or Bidahochi Formation tulate is disfavored here because deposition of et al., 2007), which underlie Huala pai Lime- parentage is not and has not been a signifi cant Hualapai Limestone was contiguous westward stone in the Temple Basin, overlap in age with factor volumetrically for net Colorado River from Grand Wash Trough into Gregg and Tem- the “rocks of Grand Wash Trough” (Bohan- sand composition. That inference is reinforced ple Basins (Blair and Armstrong, 1979; Wallace non, 1984), but their deposition continued until by the observation that modern Colorado River et al., 2005), with only limited relief on the sedi- ca. 8 Ma, ~4 m.y. after deposition of Huala- sand collected at Kwagunt Rapids (CR-1 of mented fl oor of Lake Hualapai from local algal pai Limestone had begun in the Grand Wash Fig. 1) above the junction with the Little Colo- terracing (Crossey et al., 2014). Trough (Fig. 4). Currently available age con- rado River is congruent with modern Colorado We note that projecting elevations of Huala- trols for Hualapai Limestone (Fig. 4) permit the River sands collected at Hance Rapids (CR-2 of pai Limestone across modern topography is view that Hualapai deposition was migratory, Fig. 1; P = 0.20/0.16) and Bass Rapids (CR-3 of not a reliable means for reconstructing Lake with Hualapai Limestone of the Temple Basin Fig. 1; P = 0.59/0.54) below the Colorado–Little Hualapai paleoshorelines because the modern largely or even entirely younger than Hualapai Colorado junction. distribution of Hualapai Limestone refl ects fault Limestone of the Grand Wash Trough, but we Figure 5 shows graphically the overall simi- offsets of ~275 m (Faulds et al., 2001b; Wal- discount that interpretation as less likely than larity of pre–75 Ma detrital-zircon subpopula- lace et al., 2005) across the Lost Cabin Range– incremental expansion of a lacustrine environ- tions in sands from the Virgin River depression Wheeler Ridge fault system (Fig. 2) between the ment westward over time. Thinning of Hualapai and from the Colorado River in and near the Grand Wash Trough and Gregg Basin, and of Limestone from east to west (Fig. 4) is compati- Grand Canyon, and Figure 6 shows the similari- ~125 m from the western fl ank of Gregg Basin ble with a quasi-constant net rate of limestone ties of the same age subpopulation in sands of to the eastern fl ank of Temple Basin (Fig.4). accumulation at 45–60 m/m.y. the Virgin River depression and key Colorado- Syn-Hualapai as well as post-Hualapai faulting related sands at a more regional scale. Note the is implied by fanning dips in Hualapai Lime- DETRITAL-ZIRCON DATA close matches of the peaks for detrital-zircon stone, which thickens toward bounding faults grains of Paleozoic and Precambrian ages on the of all three tilted basinal fault blocks (Crossey All available detrital-zircon samples from curves of Figure 6. We attribute the similarity et al., 2014). the Muddy Creek Formation of the Virgin River of pre–75 Ma age subpopulations in Muddy There is no direct evidence that Lake Huala- depression and the Overton Arm Basin derive Creek Formation and Colorado-related sands pai ever fl ooded the Virgin River depression, from informally named upper members of the to the recycling of detrital zircons from Paleo- where no Hualapai Limestone is known from exposed Muddy Creek succession (Forrester, zoic–Mesozoic strata of the Colorado Plateau, either the surface (Fig. 2) or the subsurface 2009; Muntean, 2012). The collected strata for essentially the entire Colorado Plateau sedi- (Fig. 3). Positing that Hualapai Limestone was were deposited during the interval from ca. mentary succession is exposed and available for deposited in the Virgin River depression, but has 6 Ma to ca. 4 Ma and are therefore all younger potential recycling within the Virgin River drain- since been removed by erosion, seems implausi- than Hualapai Limestone (Fig. 4). age basin (Rowley et al., 2008; Biek et al., 2009). ble because the surface of basin fi ll forming Unlabeled Triassic, Jurassic, and Cretaceous age the Muddy Creek Formation is as young as ca. Muddy Creek Formation peaks on Figure 6 refl ect the Mesozoic transport 4 Ma, postdating the youngest known Hualapai of detritus from the Cordilleran magmatic arc Limestone by ~2 m.y. It has been suggested Nearly all detrital-zircon grains in 13 samples along the western continental margin eastward to that the “marl of White Narrows” in the Glen- from the Muddy Creek Formation represent the Colorado Plateau, to mingle there with older dale Basin west of the Virgin River depression two distinct age subpopulations: (1) late Ceno- detrital zircons derived in large part from eastern is a record of Lake Hualapai (Spencer et al., zoic grains ≤28 Ma (10% of total grains), and and southern Laurentia (Dickinson and Gehrels, 2008b; Roskowski et al., 2010), but vertebrate (2) Cretaceous or older grains ≥81 Ma (90% 2010), and to be recycled jointly with the latter and invertebrate fossils from that unit (Schmidt of total grains). Only two grains (0.2% of 894 into modern river systems. et al., 1996) are Pliocene (5.0–4.5 Ma), at least total grains) at 34 Ma and 65 Ma fall between One of the 13 Muddy Creek samples, FTM29 a million years younger than uppermost Huala- those two age limits. The older (pre–75 Ma) of of Forrester (2009) from near the base of the

1128 Geosphere, December 2014

TABLE 1. PROBABILITY (P) VALUES FROM STATISTICAL KOLMOGOROV-SMIRNOFF (K-S) ANALYSIS OF U-Pb AGES FOR >75 MA SUBPOPULATONS OF DETRITAL ZIRCONS IN SUBSETS OF VIRGIN-RELATED AND COLORADO-RELATED FLUVIAL SANDS Virgin-related sands Colorado-related sands MeB MoB OAB MCF VPP VVR CGC HCR PCR CRR LCR BFM A. P values from K-S analysis with errors in the cumulative distribution function (CDF) MeB 0.53 0.66 0.50 0.68 0.86 0.89 0.53 0.57 0.44 0.12 0.00 0.00 MoB 0.66 0.54 0.50 0.91 0.36 0.42 0.34 0.20 0.36 0.15 0.00 0.01 OAB 0.50 0.50 0.55 0.98 0.49 0.47 0.67 0.23 0.22 0.83 0.00 0.00 MCF 0.68 0.91 0.98 0.56 0.40 0.36 0.83 0.09 0.13 0.26 0.00 0.00 VPP 0.86 0.36 0.49 0.40 0.99 0.92 0.59 0.04 0.11 0.08 0.00 0.00 VVR 0.89 0.42 0.47 0.36 0.92 0.62 0.49 0.01 0.02 0.40 0.00 0.00 CGC 0.53 0.34 0.67 0.83 0.59 0.49 0.47 0.49 0.72 0.61 0.00 0.01 HCR 0.57 0.20 0.23 0.09 0.04 0.01 0.49 0.50 0.76 0.11 0.00 0.00 PCR 0.44 0.36 0.22 0.13 0.11 0.02 0.72 0.76 0.66 0.11 0.00 0.01 CRR 0.12 0.15 0.83 0.26 0.08 0.40 0.61 0.11 0.11 0.20 0.00 0.02 LCR 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.31 0.48 BFM 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.02 0.48 0.73 B. P values from K-S analysis without errors in the cumulative distribution function (CDF) MeB 0.42 0.42 0.33 0.48 0.63 0.61 0.35 0.33 0.39 0.11 0.00 0.00 MoB 0.42 0.45 0.35 0.88 0.26 0.31 0.35 0.14 0.21 0.19 0.00 0.01 OAB 0.33 0.35 0.43 0.93 0.35 0.29 0.44 0.06 0.06 0.48 0.00 0.00 MCF 0.48 0.88 0.93 0.42 0.30 0.23 0.61 0.02 0.04 0.22 0.00 0.00 VPP 0.63 0.26 0.35 0.30 0.91 0.89 0.45 0.02 0.09 0.06 0.00 0.00 VVR 0.61 0.31 0.29 0.23 0.89 0.50 0.18 0.00 0.01 0.27 0.00 0.00 CGC 0.35 0.35 0.44 0.61 0.45 0.18 0.37 0.09 0.39 0.39 0.00 0.01 HCR 0.33 0.14 0.06 0.02 0.02 0.00 0.09 0.37 0.63 0.04 0.00 0.00 PCR 0.39 0.21 0.06 0.04 0.09 0.01 0.39 0.63 0.52 0.01 0.00 0.00 CRR 0.11 0.19 0.48 0.22 0.06 0.27 0.39 0.04 0.01 0.13 0.00 0.02 LCR 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.33 BFM 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.02 0.33 0.66 Note: N—number of samples, n—number of U-Pb ages per subset; bold print denotes P ≥ 0.05 (≤95% conﬁdence that the U-Pb ages in the paired subsets could not have been derived by random selection of detrital-zircon grains from the same parent population; italics denote mean P for comparisons of individual samples within each subset. MeB—Muddy Creek Formation of the Mesquite Basin (Forrester, 2009): F11 (BDW11), F18 (BDW 18), F36 (FTM36) plotted on Figure 2; N = 3, n = 127. MoB—Muddy Creek Formation of the Mormon Basin (Muntean, 2012): M1, M2, M3 M4 (TMSS1, 2, 3, 4) plotted on Figure 2 as M1–M4; N = 4, n = 311. OAB—Muddy Creek Formation of the Overton Arm Basin (Muntean, 2012): TMSS 5, 8, 9, 11, 12 (not plotted individually on Figure 2 for reasons of scale); N = 5, n = 356. MCF— Miocene–Pliocene Muddy Creek Formation of the Virgin River depression: Mesquite Basin + Mormon Basin + Overton Arm Basin; N = 12, n = 794. VPP—inset Pliocene– Pleistocene terraces of the Virgin River depression: F9 (P-P09 of Forrester, 2009) and M13 (TMSS13 of Muntean, 2012) plotted on Figure 2; N = 2, n = 162. VVR— modern Virgin River: 806-10 (CRT0806-10 of Kimbrough et al., 2015) and VR-20 (of Forrester, 2009) plotted on Figure 2; N = 2, n = 156. CGC—modern Colorado River in the Grand Canyon (Kimbrough et al., 2015): CR1, CR2, and CR3 plotted on Figure 1; N = 3, n = 187. HCR—Holocene lower Colorado River and delta downstream from Lake Mead (Kimbrough et al., 2015): CR5-1, CR5-2, 1-23-6-1, Yuma, San Felipito, Santa Clara; N = 6, n = 574. PCR—Pliocene lower Colorado River (Bullhead alluvium) and 4.9–3.0 Ma delta (Winker and Kidwell, 1986; Dorsey et al., 2011) downstream from Lake Mead (Kimbrough et al., 2015): two river samples (6322-6, 6322-37) and four delta samples (FC5-3, FC6-1, FC6-2, 2-4-6-1); N = 6, n = 551. CRR—Miocene Crooked Ridge River (Fig. 1), an inferred tributary of the paleo–Colorado River (Lucchitta et al., 2011, 2013); N = 5, n = 457 (data from Hereford et al., 2015). LCR—modern Little Colorado River (Kimbrough et al., 2015): 806-6 (CRT806-6 near Winslow, Arizona) and 806-7 (CRT806-7 near Cameron, Arizona) plotted on Figure 1; N = 2, n = 123. BFM—ﬂuvial Miocene Bidahochi Formation (Kimbrough et al., 2015): CRT806-12 and CRT806-13 near Sanders, Arizona, not plotted on Figure 1 (sample localities upstream off the map area); N = 2, n = 114.

exposed succession on the face of Flat Top although the exact positions of the age peaks displays a broad age peak spanning 40–22 Ma, Mesa in the Mesquite Basin, is omitted from vary because of the limited census provided by with only a minimal “shoulder” at the Muddy Table 1 and Figures 5–6 because its pre–75 Ma only 24–56 detrital-zircon grains contributing Creek peak of 19 Ma. detrital-zircon subpopulation is anomalous with to each plotted curve. By contrast, the Muddy respect to the other 12 Muddy Creek samples. Creek Formation displays a unitary age peak at Provenance Considerations P values are less than 0.025 for comparisons of 19 Ma. The total number (n = 14) of <75 Ma pre–75 Ma detrital-zircon U-Pb ages in FTM29 detrital-zircon grains in the composited subset Pederson (2008) inferred from petrographic with other Muddy Creek samples, apparently of samples from the modern Virgin River and studies that some detritus was contributed to because of a slight excess of 2000–1600 Ma Pliocene–Pleistocene terrace deposits of the Vir- the Muddy Creek Formation of the Virgin River grains in FTM29 derived from basement rocks gin River depression (VPP and VCR of Table 1) depression from Tertiary caldera complexes to exposed nearby. are too few for reliable Kolmogorov-Smirnoff the north in Nevada (Fig. 8), but our detrital- The younger (post–75 Ma) age subpopulation analysis, but they have a mean age of 20 ± 3 Ma, zircon data appear to rule out that inference in the Muddy Creek Formation of the Virgin which is indistinguishable from the unitary age except in limited measure. The unitary peak of River depression is distinctly different, however, peak for the Muddy Creek Formation. We con- 19 Ma for Muddy Creek detrital zircons does from Colorado River sands (Fig. 7). P values clude that no paleo–Colorado River sediment not permit signiﬁ cant contributions from cal- for all sample subsets, some of which must be contributed detritus to the exposed Muddy dera detritus, which should display greater age composited to achieve the minimum number of Creek Formation, which was instead depos- spreads (Fig. 9). The detrital-zircon age peak ages (n = 20) needed for reliable Kolmogorov- ited entirely by a paleo–Virgin River and its instead points to derivation of Tertiary detrital Smirnoff (K-S) statistics, are uniformly 0.00 tributaries uncontaminated by paleo–Colorado zircons dominantly from the Iron Axis igneous for all comparisons of Muddy Creek Formation River detritus. The age distribution curve for belt (Fig. 9), which includes the Pine Valley lac- samples with Colorado-related sands (Table 2). the Miocene Crooked Ridge River (Fig. 1) has colith and associated extrusive latite exposed in The latter display multiple <75 Ma age peaks a more restricted population of Cenozoic grains the upstream Virgin River drainage above the spaced quasi-uniformly from 73 Ma to 6 Ma, than the main stem of the Colorado River, but it Virgin River gorge (Fig. 8).

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Figure 5. Age distribution curves for >75 Ma detrital-zircon (DZ) ABC D E F subpopulations in sands from the A. Modern Virgin River Virgin River depression and the Virgin Gorge and Riverside (N = 2) Colorado River in and near the n = 156 (95% of total DZ grains) three grains >3000 Ma omitted Grand Canyon (see Table 1 and Figure 2 for sources of data). N is the number of samples for each B. Pliocene - Pleistocene strata Overton Arm and Littlefield (N = 2) detrital-zircon data set, and n is n = 162 (95% of total DZ grains) the number of U-Pb ages for indi- two grains >3000 Ma omitted from plot vidual detrital-zircon grains. From Kolmogorov-Smirnoff (K-S) analysis, P = 0.33–0.74 with error in the CDF (P = 0.11–0.50 without error C. Miocene - Pliocene Muddy Creek Formation in the CDF) for curve D paired (N = 12) n = 794 (90% of total DZ grains) with curves A-B-C (mean P = 0.56 ± five grains >3000 Ma omitted from plot 0.17; 0.36 ± 0.18), and P = 0.00 for curve E paired with any of the other four curves. Color bands: A—post– mid-Permian and Mesozoic, B— D. Modern Colorado River pre–mid-Permian and Paleozoic, Grand Canyon (N = 3) n = 187 (99% of total DZ grains) C—late Neoproterozoic (accreted peri-Gondwanan terranes and Rodinian rift granites), D—late E. Pliocene Colorado River Mesoproterozoic and early Neo- near the Grand Canyon (N = 2) proterozoic (Grenville orogen), E— n = 242 (86% of total DZ grains one grain >3000 Ma omitted from plot) early Mesoproterozoic (an hydrous alkalic Laurentian granites), F— 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 late Paleoproterozoic (Yavapai and Age (Ma) Mazatzal age belts).

Figure 6. Age distribution curves for >75 Ma detrital-zircon (DZ) 415 1705 subpopulations in sands from 600 A. Holocene lower Colorado River 1455 (HCR of Table 1) 1085 the Virgin River depression and N = 6 n = 575 the Colorado River system. N is the number of samples for each 435 1065 B. Modern Virgin River (VVR of Table 1) detrital-zircon data set, and n is 620 and Pliocene-Pleistocene strata (VPP of Table 1) of the Virgin River depression the number of U-Pb ages for indi- 1405 1695 N = 4 n = 318 vidual detrital-zircon grains (14

1700 detrital-zircon grains >3000 Ma or 0.5% of total detrital-zircon C. Pliocene lower Colorado River 420 1095 1430 610 (PCR of Table 1) grains are omitted from the plots). N = 8 n = 664 Numbers above curves denote the ages in Ma of key detrital-zircon age peaks: 425 ± 10 Ma (Silu-

1695 rian)—Appalachian orogen of D. Miocene-Pliocene Muddy Creek eastern Laurentia; 610 ± 10 Ma 420 1085 Formation of the Virgin River 620 1455 depression (MCF of Table 1) (Ediacaran)—Gondwanan ter- N = 12 n = 794 ranes accreted to eastern and southern Laurentia; 1070 ± 15 Ma 1715 (Stenian)—Grenville orogen of 425 E. Miocene Cooked Ridge River eastern and southern Laurentia; (CRR of Table 1) on the 1075 1450 Kaibito Plateau and White Mesa 1430 ± 25 Ma (Calymmian)— 615 N = 5 n = 457 anhydrous alkalic plutons of interior Laurentia; 1705 ± 10 Ma 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 Age (Ma) (Statherian)—combined Yavapai and Mazatzal age belts of southwest Laurentia.

1130 Geosphere, December 2014

26 A. Holocene Colorado River (HCR of Table 2) Arm Basins, respectively. The 0.3–0.8 m.y. age 17 20 N = 8 n = 27 discrepancy between Pine Valley 40Ar/39Ar ages 30 73 and Muddy Creek U-Pb ages is unexplained but 8 48 may stem from analytical imprecision or a dif- ference in the ages of presently exposed Pine 28 Valley source rocks and Pine Valley detritus that B. modern Colorado River 33 (CGC* of Table 2) 57 67 was eroded during the interval 6–4 Ma. In either 40 45 6 N = 7 n = 30 case, the minor age dichotomy (~0.5 m.y.) is not viewed here as signifi cant for provenance con- 29 siderations. 35 Samples from the Muddy Creek Formation C. Pliocene Colorado River containing signifi cant contributions of Tertiary (PCR of Table 2) detrital-zircon grains older or younger than ca. 19 N = 8 n = 56 19 Ma derive exclusively from samples collected along Beaver Dam Wash in the Mesquite Basin (Fig. 9A), for which laterally extensive 19 sources in outfl ow tuffs from the Caliente caldera and virtual point sources from the Mineral Mountain (12 ± 2 Ma), Bull Valley (ca. 22 Ma), and Big Mountain (ca. 22 Ma) intrusions (Fig. 8) are both feasible. Downstream dilution of Caliente detritus with more voluminous detritus delivered to the Virgin River depression by the main stem of the ancestral Virgin River presumably accounts for its paucity in other detrital-zir- D. Miocene-Pliocene con samples from the Virgin River depression. Muddy Creek Formation Virgin River depression Volcaniclastic detritus from the Caliente, Indian (MCF of Table 2) Peak, and Kane Spring Wash calderas (Fig. 9) N = 12 n = 100 may be present in the Muddy Creek Formation of the Glendale Basin, into which Meadow Val- ley Wash fl ows from headwaters in the caldera complexes (Fig. 8), but no detrital-zircon data 12 are currently available to test that possibility. Limited petrofacies data for the Muddy Creek Formation and the Pliocene Colorado River 24 delta are supportive of our conclusion from 27 detrital-zircon data that the Colorado River did not fl ow into the Virgin River depression during sedimentation of at least the exposed strata E. Miocene Crooked Ridge River (CRR of Table 2) of the Muddy Creek Formation (Fig. 10). The 14 N = 5 n = 24 Colorado delta sands are more feldspathic, by a factor of perhaps three, than any sampled Muddy Creek assemblages. The ratio of lithic 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 fragments to quartz mineral grains is highest for Age (Ma) the Mesquite and Glendale Basins, where the highest percentages of volcaniclastic detritus Figure 7. Age distribution curves for <75 Ma detrital-zircon (DZ) subpopulations in sands containing abundant volcanic lithic fragments from the Virgin River depression and the Colorado River system. N is the number of samples can be anticipated from subregional drainage for each detrital-zircon data set, and n is the number of U-Pb ages for individual detrital- patterns (Fig. 8). zircon grains. Numbers above curves denote the ages in Ma of key detrital-zircon age peaks. Music Mountain Formation

Slight displacement of the Muddy Creek 2009). Associated Pine Valley latite, erupted The Eocene Music Mountain Formation of detrital-zircon age peak of 19 Ma from the by ﬂ ank collapse of the Pine Valley laccolith the Hualapai and Coconino Plateaus east of the 22–20 Ma age range (Hacker et al., 2007) of (Hacker et al., 2007) and 335 m thick (Biek Grand Wash Trough contains a detrital-zircon Iron Axis intrusives and extrusives requires et al., 2009), has yielded a concordant 40Ar/39Ar population unlike that of the Muddy Creek comment. The largest Iron Axis body is the Pine age of 20.4 Ma (Biek et al., 2009). By contrast, Formation (Fig. 11B). The Music Mountain Valley laccolith, 250–300 km2 in area and 900 Muddy Creek U-Pb age peaks for detrital zir- Formation was deposited by a Paleogene drain- m thick, which has yielded 40Ar/39Ar ages of cons are 19.2 ± 0.3 Ma, 19.5 ± 0.3, and 19.7 ± age system ﬂ owing from south to north across 20.5–20.3 Ma (Hacker et al., 2007; Biek et al., 0.3 Ma in the Mesquite, Mormon, and Overton the site of the modern Grand Canyon (Fig. 1)

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TABLE 2. PROBABILITY (P) VALUES FROM STATISTICAL KOLMOGOROV-SMIRNOFF trated by the well (Fig. 3). In principle, those (K-S) ANALYSIS OF U-Pb AGES FOR <75 MA SUBPOPULATONS OF DETRITAL ZIRCONS IN SUBSETS OF VIRGIN-RELATED AND COLORADO-RELATED FLUVIAL SANDS potential repositories of paleo–Colorado River sediment can be tested by further investigations Sample Virgin-related sands Colorado-related sands subsets MeB MoB OAB MCF CGC* CRR HCR PCR of detrital-zircon populations that might record a N 3 4 513 7 5 6 6different provenance signal than the uppermost n 32 24 42 98 28 24 27 39 ~250 m of the Muddy Creek Formation. As yet % of total grains 20 20 11 11 6 5 5 7 unsampled cuttings (but not cores) from the A. P values from K-S analysis with errors in the cumulative distribution function (CDF) Mobil Virgin 1A well are available through MeB – 0.07 0.03 0.15 0.00 0.00 0.00 0.00 MoB 0.07 – 0.96 0.94 0.00 0.00 0.00 0.00 the Nevada Bureau of Mines and Geology OAB 0.03 0.96 – 0.85 0.00 0.00 0.00 0.00 (George A. Davis, 2013, personal commun.). MCF 0.15 0.94 0.85 – 0.00 0.00 0.00 0.00 CGC* 0.00 0.00 0.00 0.00 – 0.08 0.47 0.15 Our second postulate is diffi cult to evaluate CRR 0.00 0.00 0.00 0.00 0.08 – 0.50 0.03 without relevant data, but it is worth noting that HCR 0.00 0.00 0.00 0.00 0.47 0.50 – 0.09 most of the unsampled subsurface units have PCR 0.00 0.00 0.00 0.00 0.15 0.03 0.09 – lithologies suggestive of internal drainage dif- B. P values from K-S analysis without errors in the cumulative distribution function (CDF) fi cult to reconcile with fl ooding of the Virgin MeB – 0.03 0.02 0.09 0.00 0.00 0.00 0.00 MoB 0.03 – 0.52 0.35 0.00 0.00 0.00 0.00 River depression by a major regional river. The OAB 0.02 0.52 – 0.59 0.00 0.00 0.00 0.00 basal 215 m of Muddy Creek Formation pene- MCF 0.09 0.35 0.59 – 0.00 0.00 0.00 0.00 trated by the well are described as “gypsiferous,” CGC* 0.00 0.00 0.00 0.00 – 0.01 0.29 0.09 CRR 0.00 0.00 0.00 0.00 0.01 – 0.07 0.00 suggestive of playa deposition and leaving only HCR 0.00 0.00 0.00 0.00 0.29 0.07 – 0.05 the middle 420 m of Muddy Creek Formation PCR 0.00 0.00 0.00 0.00 0.09 0.00 0.05 – in the subsurface as an attractive candidate for Note: See Table 1 for explanation of acronyms and conventions used for tabulation and identifi cation of subsets except to achieve the requisite ≥20 U-Pb ages for reliable K-S comparisons. CGC* equals CGC plus riverine deposition that might have included a Pliocene samples LMSP2 and H5HW of Colorado River sediment (Kimbrough et al., 2015) collected along the contribution of paleo–Colorado River sediment. shores of Lake Mead (Fig. 2) and samples CRT806-4 and CRT806-5 from the modern San Juan River upstream The syn-Hualapai (12–10 Ma) “red sandstone from Figure 1 at Bluff, Utah, and Mexican Hat, Utah, respectively (Kimbrough et al., 2015). N—number of samples; n—number of U-Pb ages per subset. unit” (Fig. 4) underlying Muddy Creek Forma- tion in the well bore (Fig, 3) is interpreted as largely playa lake and eolian deposits (Bohan- toward the Claron depocenter in southern Utah is present in the exposed Muddy Creek For- non, 1984), and it is unattractive as a possible (Fig. 1) before dissection of the Colorado Pla- mation of the Virgin River depression and the record of riverine sedimentation. The Horse teau led to Neogene evolution of the Colorado associated Overton Arm Basin, as others have Spring Formation below the “red sandstone River (Cather et al., 2012). In common with concluded on various grounds (Pederson, 2001, unit” (Fig. 3) is a heterogeneous assemblage mid-Cretaceous to mid-Miocene sedimentary 2008; Kimbrough et al., 2015). The only local of alluvial and lacustrine deposits interpreted assemblages across the breadth of the southern exposures not adequately sampled for detrital as the record of locally developed basins of Colorado Plateau from the Grand Canyon region zircons are strata of the informally named lower internal drainage fi lled with sediment derived eastward into New Mexico, the Music Moun- member (Muntean, 2012) of the Muddy Creek from bounding uplands or deposited in basinal tain Formation was derived dominantly from succession. We also have no detrital-zircon data lakes that developed downslope from clastic Precambrian basement of central Arizona. For from the Glendale Basin west of the Virgin aprons shed from bounding uplands (Bohan- multiple assemblages of that provenance fam- River depression, but it seems illogical to sup- non, 1983, 1984; Lamb et al., 2005). Strata of ily (Fig. 11), dual U-Pb age peaks for detrital pose that paleo–Colorado River sediment could the Horse Spring Formation encountered in the zircons are dominant and not infl uenced by any have reached the Glendale Basin if it is not test well (Bohannon et al., 1993) include only notable sediment recycling from Paleozoic– present within the Virgin River depression. The the uppermost Lowell Wash Member, dated Mesozoic plateau strata: (1) Paleoproterozoic observational constraints lead to four postulates: elsewhere at 14–12 Ma (Harlan et al., 1998; (1745–1655 Ma), refl ecting derivation from First, if the detrital-zircon data from the Beard et al., 2007; Lamb et al., 2010), and the the Yavapai and Mazatzal orogenic belts of post-Hualapai (<6 Ma) Muddy Creek Forma- lowermost Rainbow Gardens Member, dated the Mogollon Highlands and descendants, and tion are assumed from their overall congruence elsewhere at 24–18 Ma (Beard, 1996; Beard (2) Mesoproterozoic (1445–1385 Ma), refl ecting to be representative of the entire Muddy Creek et al., 2007, 2010), suggesting that an intrafor- derivation from younger granitic plutons intru- Formation (≤10? Ma), then no paleo–Colorado mational unconformity spanning ~5 m.y. breaks sive into Yavapai–Mazatzal wall rocks. Deriva- River entered the Virgin River depression during the Horse Spring succession in the subsurface tion of the Precambrian detritus from the south is Muddy Creek sedimentation. of the Virgin River depression. That inference confi rmed in the case of the Mogollon Rim For- Second, if a syn-Hualapai (12–6 Ma) or pre- challenges the notion that a major regional river mation (Fig. 11C) by the presence of 21–18 Ma Hualapai paleo–Colorado River entered the Vir- delivering a steady input of voluminous sedi- detrital zircons (n = 5), presumably derived from gin River depression before sampled horizons ment could be responsible for deposition of any the Superstition volcanic fi eld (McIntosh and of the Muddy Creek Formation were depos- Horse Spring strata present in the subsurface Ferguson, 1998; Potochnik et al., 2012). ited, then its sediment load must be present in beneath the Virgin River depression. (1) unsampled older Muddy Creek horizons Third, if no detrital-zircon signal of paleo– WIDER PERSPECTIVES exposed near Overton Arm (Muntean, 2012), Colorado River sediment is found in subsurface (2) unexposed lower Muddy Creek Formation units of the Virgin River depression, then the Despite previous tentative arguments (Dick- known only from cuttings in the Mobil Virgin concept of either syn-Hualapai or pre-Hualapai inson, 2013), our detrital-zircon U-Pb data dem- River 1A well of the Mormon Basin (Bohannon paleo–Colorado River fl ow across the Kaibab onstrate that no paleo–Colorado River sediment et al., 1993), or (3) pre–Muddy Creek strata pene- uplift and into the Virgin River paleodrainage

1132 Geosphere, December 2014

114° W TERTIARY IGNEOUS CENTERS Iron Axis igneous centers limit of Virgin Tpv - Pine Valley laccolith - latite drainage basin Tbm - Big Mountain Tbv - Bull Valley Tmm - Mineral Mountain streams of Virgin drainage basin KSC Kane Springs Wash caldera

IPCC limit of Caliente outﬂow tuffs (C) Figure 8. Distribution of cal- selected towns 38° N 38° N CCC Caliente caldera complex deras and other igneous centers Pi 115° W limit of Indian Peak that potentially contributed outﬂow tuffs (IP) W Pa detritus to the Muddy Creek V M Indian Peak caldera Formation. Streams: AC—Ash IPCC complex Creek, BDW—Beaver Dam IP Wash, CW—Clayhole Wash, H C 113° W HD—Hurricane Draw, KSW— CCC Tbm Kane Spring Wash, MR— Tbv Muddy River (below junction A Tmm

R C of MVW and PW), MVW— P V KSC A W Meadow Valley Wash, PW— Tpv Pahranagat Wash, SC—Short SCR S SF W W T SG Creek, SCR—Santa Clara S B K D River, SF—South Fork (of Vir- C W SC gin River), TW—Toquop Wash, 37° N 37° N R CC VR—Virgin River. Towns: MeB V Me A—Alamo, C—Caliente, CC— C Colorado City, Pa—Panaca, W TMB MoB Pi—Pioche, H—Hiko, Me— Mo

D Mesquite, Mo—Moapa, S— M Springdale, SG—St. George. N GB R

OAB 113° W

Muddy Creek Formation GB - Glendale Basin 50 km MeB - Mesquite Basin MoB - Mormon Basin OAB - Overton Arm Basin 115° W Lake Mead 114° W TMB - Table Mesa Basin

may be invalid. That perspective is diffi cult to the cutting of a paleocanyon across the Kaibab steep narrow canyon that may not have formed reconcile, however, with several observations: uplift by a paleo–Colorado River; and (3) analy- until a stream working headward from the Vir- (1) Projection of the Crooked Ridge River and sis of overall Grand Canyon geomorphology by gin River depression had broken through the Bidahochi fl uvial systems of northern Arizona Pelletier (2010) suggests that river fl ow through rim of the Colorado Plateau, fl exed upward (Fig. 1) downstream from known outcrops sug- the western Grand Canyon could have been by structural unloading along the Piedmont gests that both descended to an elevation near triggered by a stream working headward from fault (Fig. 2), which bounds the Virgin River 1625 m near the confl uence of the modern the Grand Wash Trough to capture the paleo– depression on the east. Incorporation of the Colorado and Little Colorado Rivers (Dickin- Colorado River at ca. 6 Ma in the area of the headwaters of the Virgin River into a drainage son, 2013), and from that spatial position, fl ow- modern central Grand Canyon midway along system integrated into the Virgin River depres- age of a paleo–Colorado trunk stream across its postulated course across the Shivwits Pla- sion may have been a later development than the Kaibab uplift at an elevation near the top teau from the Kaibab uplift to the Virgin River paleo–Colorado River fl ow into upper reaches of the Redwall Limestone, ~750 m above the paleodrainage. of the Virgin River paleodrainage. A potential fl oor of the modern eastern Grand Canyon, is Fourth, fl owage of a paleo–Colorado River alternate exit of a postulated paleo–Colorado the most attractive paleogeomorphic inference; crossing the Kaibab uplift into the Virgin River River from the upper Virgin drainage is pro- (2) thermochronologic analysis suggests that the paleodrainage does not necessarily require exit vided by Kanarraville gap (Fig, 1), which leads eastern Grand Canyon was cut to half its pres- of that river into the Virgin River depression. into the Great Basin north of the Virgin River ent depth during the interval 25–15 Ma (Lee The Virgin River now enters the Virgin River depression. The gap is now blanketed by a thin et al., 2013), an inference fully compatible with depression through the Virgin River gorge, a veneer of Neogene sediment overlying strata of

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22–27 Marysvale volcanic center (central Utah)

21–32 Indian Peak caldera complex and outﬂow tuffs

13–14 18–26 Caliente caldera complex and outﬂow tuffs

13–16 Kane Springs Wash caldera

Mineral Pine Valley laccolith and latite Mountain Figure 9. Age distribution curves 10–14 20–22 (bottom) for <35 Ma detrital- Iron Axis intrusives and extrusives zircon grains in the Muddy 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Creek Formation compared to the ages of potential igneous sources (top). See Figure 8 for 19 locations of the igneous centers. Ma A. Muddy Creek Formation of the Mesquite Basin (two N = 4 samples of Forrester (2009) The ages of the igneous centers grains) n = 36 detrital zircon grains (14% of total) are adapted after Best et al. (1989, 1993, 2013), Biek et al. 19 Ma (2009), Grommé et al. (1997), Hacker at al. (2007), Noble and McKee (1972), Novak (1984), Novak and Mahood (1986), B. Muddy Creek Formation of the Mormon Basin Rowley et al. (1994, 1995), and N = 4 samples of Muntean (2010) Scott et al. (1995). n = 24 detrital zircon grains (7% of total)

(one grain)

19 Ma

C. Muddy Creek Formation of the Overton Arm Basin N = 5 samples of Muntean (2010) n = 38 detrital zircon grains (10% of total) (one grain)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 Age (Ma)

the Jurassic Glen Canyon Group (Rowley et al., by which to reconcile the lack, to date, of any CONCLUSIONS 2008; Biek et al., 2009). detrital-zircon evidence for paleo–Colorado fl ow- If Kanarraville gap is accepted as a potential age into the Virgin River depression with consid- U-Pb ages for detrital zircons collected from route for paleo–Colorado River fl ow, then the erations of regional drainage evolution. Flowage exposed horizons of the Miocene–Pliocene Miocene Colorado River may have been tributary of a paleo–Colorado River into and through the Muddy Creek Formation preclude fl owage of to the postulated Bell River of Sears (2013) fl ow- Pacifi c Northwest as an upstream tributary of the a 6–4 Ma paleo–Colorado River into the Vir- ing across Laurentia through the eastern Great Bell River might explain the observation that fos- gin River depression during deposition of the Basin and the Pacifi c Northwest toward a termi- sil fi shes of the Miocene Bidahochi Formation youngest ~250 m of the Muddy Creek Forma- nus at Saglek Basin of the Labrador Sea in north- (Fig. 1) have close biotic affi nities with fossil tion. All the sampled strata were deposited after east Canada. That hypothesis is beyond the scope fi shes related to the Snake River in the Pacifi c ca. 6 Ma during a time frame when the Colorado of this paper to address, but it offers one means Northwest (Spencer et al., 2008a). River was already fl owing through the western

1134 Geosphere, December 2014

Winker (1987) Pederson (2008) Qm Overton Arm basin Forrester (2009) ) Muntean (2010) 7 = (N

Mormon Figure 10. Upper three-quarters (Qm > (N = basin 3) 25%) of a Qm-F-Lt petrofacies diagram of the mean modal compositions (symbols) 75 75 25 25 of Miocene–Pliocene sandstones from the Pliocene Muddy Creek Formation (Glendale, Mes- Colorado (N Mormon = 4) basin quite, Mormon, and Overton Arm Basins) River delta and Pliocene sandstones from ancestral 7) ( = N (N Glendale Colorado River deltaic deposits exposed = 1 0) basin in southern California (Dorsey et al., 2007, 1) 2011). N is the number of thin sections point (N = counted for each sample set plotted, and 50 50 hexagons surrounding symbols for mean 50 50 compositions delimit standard deviations Mesquite basin (N = 15) for each sample set. ( N = 1)

50 25 25 50

F 25% Qm Lt

1385

A. Miocene “rocks (strata) of N = 4 n = 320 Grand Wash trough” 94% of DZ grains are 1300–1800 Ma 1745 (Bohannon, 1984) (one DZ grain >3000 Ma omitted)

1695

1405 N = 2 n = 196 B. Eocene Music Mountain Formation Hualapai and Coconino Plateaus 93% of DZ grains are 1300–1800 Ma

1655

1445 N = 1 n = 97 C. Miocene Mogollon Rim Formation 83% of DZ grains are 1300–1800 Ma near Show Low, Arizona

1695 N = 4 n = 402 75% of DZ grains are 1300–1800 Ma 1425 D. Oligocene Chuska Sandstone (one DZ grain >3000 Ma omitted) Chuska Mountains

1725 E. Toreva and Gallup Formations N = 2 n = 173 [Turonian Upper Cretaceous] 80% of DZ grains are 1300–1800 Ma 1440 Black Mesa and San Juan Basins

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 Age (Ma)

Figure 11. Age distribution curves for detrital zircons (DZ) in mid-Cretaceous to mid-Miocene sands of Yavapai–Mazatzal provenance on the southern Colorado Plateau. N is the number of samples for each detrital-zircon data set, and n is the number of U-Pb ages for individual detrital-zircon grains. Sources of data: A—Crossey et al. (2014), B—Dickinson et al. (2012), C—Potochnik et al. (2012), D—Supplemental File (see text footnote 1; partial data in Dickinson et al., 2010), E—Dickinson and Gehrels (2008). Color bars highlight anorogenic granite (1445–1385 Ma) and Yavapai-Mazatzal (1745–1655 Ma) age peaks.

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Grand Canyon into the Grand Wash Trough, United States, Volume II: Cascades and Intermoun- Grand Canyon region over the past 12 million years: tain West: New Mexico Bureau of Mines and Mineral Geosphere, doi:10 .1130 /GES001073 .1 (in press). 75 km to the south (Fig. 2). If a pre–6 Ma Resources Memoir 47, p. 91–133. Dickinson, W.R., 2013, Rejection of the lake spillover model paleo–Colorado River fl owed into the Virgin Best, M.G., Scott, R.B., Rowley, P.D., Swadley, W.C., for initial incision of the Grand Canyon, and discussion River depression before deposition of exposed Anderson, R.E., Grommé, S.C., Harding, A.E., Deino, of alternatives: Geosphere, v. 9, p. 1–20, doi:10 .1130 A.L., Christiansen, E.H., Tingey, D.G., and Sullivan, /GES00839 .1 . Muddy Creek Formation, then the detrital- K.M., 1993, Oligocene–Miocene caldera complexes, Dickinson, W.R., and Gehrels, G.E., 2008, Sediment deliv- zircon record of its infl uence is hidden from ash-fl ow sheets, and tectonism in the central and south- ery to the Cordilleran foreland basin: Insights from view in older unsampled subsurface strata of the eastern Great Basin, in Lahren, M.M., Trexler, J.H., Jr., U-Pb ages of detrital zircons in Upper Jurassic and and Spinosa, C., eds., Crustal Evolution of the Great Cretaceous strata of the Colorado Plateau: American Muddy Creek Formation or of underlying Mio- Basin and Sierra Nevada: Reno, Nevada, Mackay Journal of Science, v. 308, p. 1041–1082. cene strata penetrated by the Mobil Virgin 1A School of Mines (University of Nevada)–Geological Dickinson, W.R., and Gehrels, G.E., 2010, Insights into Society of America (joint Cordilleran/Rocky Mountain North American paleogeography and paleotectonics test well in the Mormon Basin (Fig. 3). If that Sections meeting) Field Trip Guidebook, p. 285–311. from U-Pb ages of detrital zircons in Mesozoic strata potential evidence for paleo–Colorado River Best, M.G., Christiansen, E.H., Deino, A.L., Grommé, S., of the Colorado Plateau, USA: International Journal fl ow is tested and found also to be negative, then Hart, G.L., and Tingey, D.G., 2013, The 36–18 Ma of Earth Sciences, v. 99, p. 1247–1265, doi: 10 .1007 Indian Peak–Caliente ignimbrite fi eld and calderas, /s00531 -009 -0462 -0 . the alternatives are to abandon the postulate of southeastern Great Basin, USA: Multicyclic super- Dickinson, W.R., Cather, S.M., and Gehrels, G.E., 2010, paleo–Colorado River fl ow across the Kaibab eruptions: Geosphere, v. 9, p. 864–950, doi: 10 .1130 Detrital zircon evidence for derivation of arkosic sand uplift and the Shivwits Plateau into the Virgin /GES00902 .1 . in the eolian Narbona Pass Member of the Chuska Biek, R.F., Rowley, P.D., Hayden, J.M., Hacker, D.B., Willis, Sandstone from Precambrian basement rocks in cen- River paleodrainage, or to infer that the paleo– G.C., Hintze, L.F., Anderson, R.E., and Brown, K.D., tral Arizona, in Fassett. J.E., Zeigler, K.E., and Lueth, Colorado River exited into the Great Basin from 2009, Geologic Map of the St. George and Part of the V.W., eds., Geology of the Four Corners Country: New Clover Mountains 30′ × 60′ Quadrangles, Washington Mexico Geological Society 61st Annual Field Confer- upper reaches of the Virgin River paleodrainage and Iron Counties, Utah: Utah Geological Survey Map ence, p. 125–134. through Kanarraville gap ~100 km north of the 242, scale 1:100,000 with 101 p. text and fi gures. Dickinson, W.R., Lawton, T.F., Pecha, M., Davis, S.J., Virgin River depression. Billingsley, G.H., 1995, Geologic Map of the Littlefi eld Gehrels , G.E., and Young, R.A., 2012, Provenance of Quadrangle, Northern Mohave County, Arizona: U.S. the Paleogene Colton Formation (Uinta Basin) and Cre- Geological Survey Open-File Report 95–559, scale taceous–Paleogene provenance evolution in the Utah ACKNOWLEDGMENTS 1:24,000. foreland: Evidence from U-Pb ages of detrital zircons, Blair, W.N., 1978, Gulf of California in the Lake Mead paleocurrent trends, and sandstone petrofacies: Geo- A preliminary version of this paper was presented area of Arizona and Nevada during late Miocene time: sphere, v. 8, p. 854–880, doi: 10 .1130 /GES00763 .1 . at the 2013 Denver meeting of the Geological Society American Association of Petroleum Geologists Bulle- Dickinson, W.R., Karlstrom, K.E., Grove, M.J., Hanson, of America (Dickinson et al., 2013). We have bene- tin, v. 62, p. 1159–1170. A.D., Gehrels, G.E., Pecha, M., Cather, S.M., Crossey, fi ted from stimulating discussions of Colorado River Blair, W.N., and Armstrong, A.K., 1979, Hualapai Lime- L.J., Kimbrough, D.L., and Muntean, T., 2013, Detrital history with L.S. Beard, R. Hereford, C.A. Hill, K.A. stone Member of the Muddy Creek Formation: The zircon evidence for and against fl owage of an ancestral Howard, R.V. Ingersoll, Wayne Ranney, S.U. Janecke, Youngest Deposit Predating the Grand Canyon, South- Miocene Colorado River into the Virgin depression: Andre Potochnik, J.E. Spencer, and J.W. Sears. We eastern Nevada and northwestern Arizona: U.S. Geo- Geological Society of America Abstracts with Pro- logical Survey Professional Paper 1111, 14 p. grams, v. 45, no. 7, p. 400. also acknowledge support from National Science Blythe, N., Umhoefer, P.J., Duebendoerfer, E.M., McIntosh, Dorsey, R.J., Fluette, A., McCougall, K., Housen, B.A., Foundation grant EAR-1202428 (to Karlstrom and W.C., and Peters, L., 2010, Development of the Salt Janecke, S.U., Axen, G.J., and Shirvell, C.R., 2007, Crossey). 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