Upper Triassic Chinle Formation) and Detrital U-Pb Zircon Data from the Sonsela

Research Paper

GEOSPHERE Regional correlation of the Sonsela Member (Upper Triassic Chinle Formation) and detrital U-Pb zircon data from the Sonsela

GEOSPHERE, v. 15, no. 4 Sandstone bed near the Sonsela Buttes, northeastern Arizona, USA, https://doi.org/10.1130/GES02004.1 support the presence of a distributive fluvial system 7 figures; 1 table; 1 supplemental file Adam D. Marsh1,2, William G. Parker1, Daniel F. Stockli2, and Jeffrey W. Martz3 1 CORRESPONDENCE: [email protected] Petrified Forest National Park, Division of Science and Resource Management, 1 Park Road #2217, Petrified Forest, Arizona 86028, USA 2The University of Texas at Austin, Jackson School of Geosciences, 2305 Speedway Stop C1160, Austin, Texas 78712, USA 3The University of Houston-Downtown, Department of Natural Sciences, 1 Main Street Room 813-North, Houston, Texas 77002, USA CITATION: Marsh, A.D., Parker, W.G., Stockli, D.F., and Martz, J.W., 2019, Regional correlation of the Sonsela Member (Upper Triassic Chinle Formation) and detrital U-Pb zircon data from the Sonsela Sandstone bed ■■ ABSTRACT progradation of these distributive systems may provide important clues as to near the Sonsela Buttes, northeastern Arizona, USA, support the presence of a distributive fluvial system: how depositional rates are linked to the tectonic history of basin subsidence Geosphere, v. 15, no. 4, p. 1128–1139, https://doi.org The Sonsela Sandstone bed was first named as an informal unit in the and source uplift (Kuhlemann and Kempf, 2002). /10.1130/GES02004.1. lower part of the Chinle Formation in northern Arizona, USA, and it was later The Upper Triassic (Norian–Rhaetian) Chinle Formation consists of silici- assigned a type section near the Sonsela Buttes, where it is composed of two clastic sediments deposited primarily by fluvial, lacustrine, and paludal sys- Science Editor: Shanaka de Silva prominent sandstone units separated by a predominately siltstone unit. The tems (Blakey and Gubitosa, 1983; Dubiel and Hasiotis, 2011) on the landward Associate Editor: Christopher J. Spencer Sonsela Sandstone bed has been correlated to a number of specific sandstones side of the Cordilleran volcanic arc (Howell and Blakey, 2013; Ingersoll, 2012;

Received 26 April 2018 within the thicker, formal Sonsela Member at Petrified Forest National Park in Riggs et al., 2016). The Cordilleran arc was an important source of sediment Revision received 30 January 2019 northern Arizona. Here, we present the first detrital U-Pb zircon data for the transported east and northeast across Arizona, USA, to feed the northwesterly Accepted 29 March 2019 Sonsela Sandstone bed at the Sonsela Buttes to hypothesize the maximum flowing Chinle stem fluvial system (Riggs et al., 2012, 2013, 2016). Compared deposition age of that unit (216.6 ± 0.3 Ma) that are consistent with the pro- with the Chinle stem river, the drastic differences in drainage direction for Late Published online 8 May 2019 posed lithostratigraphic correlation with the fossiliferous Jasper Forest bed of Triassic fluvial systems across Arizona, combined with their relative proximity the lower part of the Sonsela Member at the Park. These results are corrobo- to the arc sediment sources, raises the possibility that they were distributive rated by previous high-resolution U-Pb dates and detrital zircon provenance fluvial systems (sensu Weissmann et al., 2010, 2015). studies from Petrified Forest National Park and similar sections in northern Trendell et al. (2012) advocated such an interpretation for the Sonsela Mem- Arizona and western New Mexico, USA. The hypothesized chronostratigraphic ber (sensu Lucas, 1993; Heckert and Lucas, 2002; Woody, 2006; Martz and correlation of these sandstones throughout northern Arizona permits the Parker, 2010), a coarse-grained unit of the Chinle Formation that was deposited recognition of diachronous facies distributions in the lower part of the Chinle across northern Arizona by low- to high-sinuosity fluvial systems (Howell and Formation as these coarse sediments prograded from the southwest into a Blakey, 2013). Trendell et al. (2012) argued that the sediments of the uppermost continental basin already receiving finer-grained fluvial sediments from the Blue Mesa Member and overlying Sonsela Member were deposited by a large southeast. The new age data corroborate the Norian age designation for fluvial fan that prograded northeast across Arizona away from the Cordilleran the Sonsela Member (and the Sonsela Sandstone bed) and suggest that the arc, resulting in a coarsening upwards sequence being deposited in Petrified Sonsela Sandstone bed at the Sonsela Buttes is within the Adamanian land Forest National Park (PEFO), after 220 Ma (Ramezani et al., 2014). This inter- vertebrate estimated holochronozone. pretation is also supported by the radiating dispersal pattern of Late Triassic detrital zircon in the Sonsela Member at PEFO and the Vampire Formation and Waterman Formation in southern Arizona from a source in what is now the ■■ INTRODUCTION Mojave Desert (Riggs et al., 2013). In this paper, we present new U-Pb data for the type section of the Sonsela Sandstone bed, a unit that may be correlative Prograding facies in terrestrial environments are likely to be associated with part of the Sonsela Member of PEFO, and discuss the implications for with large distributive fluvial systems (“megafans”) that form most of the sed- tracing the progradation of the Sonsela distributive fluvial system. This paper is published under the terms of the iment volume of modern continental basins, and which draw their sediments The Sonsela Sandstone bed was informally described as a course-grained CC‑BY-NC license. directly from upland sources (Weissmann et al., 2010, 2015). Calibrating the unit within the Chinle Formation (Kiersch, 1955) but later was designated a

GEOSPHERE | Volume 15 | Number 4 Marsh et al. | Regional correlation of the Sonsela Member, Chinle Formation Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/4/1128/4800442/1128.pdf 1128 by guest on 25 September 2021 Research Paper

type locality near the Defiance Uplift in the Navajo Nation of northern Arizona Martz and Parker, 2010) contains many of the enormous silicified Triassic pet- (Akers et al., 1958; Fig. 1) where it stands out prominently as two ledge-forming rified logs after which PEFO is named. This bed occurs in a thick sandstone se- sandstones in the middle of otherwise slope-forming, fine-grained siltstones quence that spans potentially as much as 9 m.y. (Ramezani et al., 2011; Atchley (Fig. 2). The Sonsela Sandstone bed was elevated to member-status within et al., 2013; Kent et al., 2018; Olsen et al., 2018) and its correlation to the type the Chinle Formation from work on stratigraphic sections at PEFO (Lucas, Sonsela Sandstone bed is not agreed upon by all workers (e.g., Lucas, 1993; 1993; Heckert and Lucas, 2002; Woody, 2006), but the correlation between the Heckert and Lucas, 2002; Woody, 2006). The age of the Sonsela Sandstone “Sonsela Sandstone bed” at its type locality and the fossiliferous subunits of bed at its type section could provide circumstantial support for the correlation the “Sonsela Member” at PEFO has been exclusively based on the lithology with a given sandstone unit within the Sonsela Member of PEFO, although it is and stratigraphic relationship of these units. important to emphasize that lithostratigraphic units can be diachronous. Here The Sonsela Member at PEFO contains numerous sandstone units, the most we report the first detrital U-Pb zircon data from the Sonsela Sandstone bed prominent of which is the Jasper Forest bed. The Jasper Forest bed (sensu from its type locality that are consistent with the correlation of the Sonsela Sandstone bed with the Jasper Forest bed of the Sonsela Member at PEFO.

100 km 109.0452°W 36.9990°N

I-15 CP20 Nomenclature Associated with the Sonsela Sandstone Bed A’ I-25 We refer to the siliciclastic unit at the Sonsela Buttes between the un- Sonsela Sandstone SMC/Fort Wingate bed type locality derlying Bluewater Creek Member and overlying Petrified Forest Member of I-40 I-40 Flagstaff the Chinle Formation as the “Sonsela Sandstone bed” in order to retain its Albuquerque A historical use. The Sonsela Sandstone bed was originally named as an infor- St. Johns I-17 Chinde Mesa mal lithostratigraphic unit prior to the adoption of standardized stratigraphic Pilot Rock nomenclature (NACSN, 2005), but it was determined to be a scientifically I-10 Phoenix and economically meaningful unit (Kiersch, 1955), and it was described and I-40 assigned a type section (Akers et al., 1958). The Sonsela Sandstone bed at its I-8 Chinde Point type locality is composed of three lithological facies, and it was correlated with I-10 Tucson other sandstone beds (described below) throughout the region. We refer to I-19 KWI the formal “Sonsela Member” at PEFO as named by Lucas (1993) and defined by Woody (2003, 2006) and Martz and Parker (2010). The Devil’s Playground The Sonsela Member at PEFO includes five major units (Martz and Parker, 2010): the Camp Butte beds, the Lot’s Wife beds, the Jasper Forest bed, the Jim Camp Wash beds, and the Martha’s Butte beds. The Jasper Forest bed is N considered the stratigraphic equivalent of the Kellogg Butte bed in the Devil’s SBJ The Tepees Playground and the Rainbow Forest bed near the Rainbow Forest Museum, Blue Mesa PEFO, Arizona (Martz and Parker, 2010; Parker and Martz, 2011; Martz et al., 2012). 5 km Agate Mesa

Private or State Trust Land Crystal Previous Lithostratigraphic Correlations of the Sonsela GPU, GPL Forest Petrified Forest National park Sandstone Bed

Park Road US-180 The “Sonsela” bed (Kiersch, 1955, p. 5) was informally designated as a Rainbow Forest Administrative Boundary sandier division of the Petrified Forest Member of the Chinle Formation as Sample it was recognized at the time. This was later named the “Sonsela sandstone bed” (Akers et al., 1958, p. 89) and was described and assigned a type section Figure 1. Map of Arizona and New Mexico, USA and the Petrified Forest National Park with detri- soon after to define a sandstone interval that divided the lower part of Herbert tal zircon samples from the Sonsela Member at the Park labeled CP20, GPL, GPU, KWI, SBJ, and Gregory’s “Division C” of the Chinle Formation (Gregory, 1917, p. 43) into up- SMC. CP20 is the sample from the Sonsela Sandstone from Dickinson and Gehrels (2008, 2010) and SMC represents the sample from the lower part of the Sonsela Member at Six Mile Canyon, per and lower parts of what was at that time referred to the Petrified Forest New Mexico (Irmis et al., 2011). Member (Gregory, 1950; Cooley, 1957; Harshbarger et al., 1957).

number of individual sandstone lenses (Akers et al., 1958; Repenning et al., 10 cm 1969; Stewart et al., 1972). The Sonsela Sandstone bed at PEFO was raised to member-status (Lucas, 1993), but the Sonsela Member was restricted only to the conglomeratic Sonsela sandstone capping Blue Mesa, between the Painted Desert Member and sandstone bed Bluewater Creek Member Blue Mesa Member within the Petrified Forest Formation of the Chinle Group. Although the wholesale status elevation of these units has not been widely accepted, most authors agree that the Sonsela Member is lithologically distinct at PEFO and is sufficiently widespread in the region to warrant member-status within the Chinle Formation (Raucci et al., 2006; Woody, 2006; Martz and Parker, 2010). In an attempt to correlate the Sonsela Member as it occurs at PEFO to the three-part Sonsela Sandstone bed at its type locality, Heckert and Lucas (2002) upper sandstone divided the Sonsela Member at the park into an upper sandstone (the Agate Sonsela * Bridge bed), a middle silty unit (the Jim Camp Wash beds), and a lower sand- Sandsttone stone (the Rainbow Forest bed). This tripartite division of the Sonsela Member was also hypothesized independently by Woody (2006) with a slightly different bed middle siltstone nomenclature provided (i.e., the Rainbow Forest beds, Jim Camp Wash beds, and Flattops One bed). Unfortunately, many of the correlations for the major sandstones in previous studies (e.g., Heckert and Lucas, 2002) were not ac- curately determined in the field or by walking out laterally extensive contacts llower sandstone between outcrop areas throughout the park, or by detailed mapping (Martz and Parker, 2010; Parker and Martz, 2017). Revisions to these correlations are summarized elsewhere (Raucci et al., 2006; Woody, 2006; Martz and Parker, 2010; Parker and Martz, 2011; Martz et al., 2012), but it is worth noting here Bluewawater Creek Member that beds correlated across PEFO by Heckert and Lucas (2002) to their type sections of the Rainbow Forest bed and Agate Bridge bed are correlative to Figure 2. Photographs of the Sonsela Sandstone bed at its type locality in northeastern Ari- the Jasper Forest bed as used here (Martz and Parker, 2010). zona, USA. (A) Type section of the Sonsela Sandstone bed looking west toward the Lukachukai The most current consensus divides the Sonsela Member at Petrified Forest Mountains. (B) Trough crossbeds and volcaniclastic cobbles within the upper sandstone unit of the Sonsela Sandstone bed. (C) Type section of the Sonsela Sandstone bed showing the two National Park into five units, the Camp Butte beds, the Lot’s Wife beds, the Jas- sandstones within it. The asterisk (*) indicates the horizon sampled for detrital U-Pb zircon. per Forest bed, the Jim Camp Wash beds, and the Martha’s Butte beds (Fig. 3; Martz and Parker, 2010; Martz et al., 2012). Using this framework, the Sonsela Sandstone bed at the Sonsela Buttes is correlated with the Jasper Forest bed At its type section a few kilometers east of Canyon DeChelly National at PEFO (Raucci et al., 2006, p. 158; Martz and Parker, 2010; Martz et al., 2012; Monument, Arizona at the Sonsela Buttes (Figs. 1 and 2), the Sonsela Sand- Atchley et al., 2013). These correlations were primarily based on lithological stone bed was thought to overly the lower part of the Petrified Forest Member similarity of the Jasper Forest bed/Rainbow Forest bed/Kellogg Butte bed with (Akers et al., 1958; Repenning et al., 1969; Stewart et al., 1972), but is now the upper sandstone at the type location of the Sonsela Sandstone bed (i.e., understood to overly the silty mudstone of the Bluewater Creek Member (in- fining-upward, quartzose, fluvial trough cross-bedded sandstones containing formally the “lower red member”; Martz and Parker, 2010; Irmis et al., 2011) limestone and chert clasts and silicified petrified logs), as well as the park- and is composed of three major divisions: a lower light gray sandstone, a wide superpositional relationships of those named sandstone units to the Lot’s middle blue-gray siltstone, and an upper, thicker light gray sandstone. These Wife beds and Jim Camp Wash beds below and above them, respectively, and sandstones, especially the upper ledge-forming unit, are trough cross-bedded; historical use (e.g., Cooley, 1957; Lucas, 1993). the coarse bedloads contain volcanic clasts and chert cobbles that preserve Correlations of the Sonsela Sandstone bed at its type locality with any of Permian macrofossils similar to those found in the Kaibab Formation (Fig. the variable sandstone-dominated units of the middle of the Chinle Formation 2B; McKee, 1937; Akers et al., 1958; Stewart et al., 1972). Where it crops out in the vicinity of PEFO have been ambiguous. Previous authors (e.g., Cooley, over 62,000 km2 of northeastern Arizona and northwestern New Mexico, the 1957; Billingsley, 1985; Heckert and Lucas, 2002) agreed that the sandstone Sonsela Sandstone bed is between 15 and 60 m thick and includes a variable capping Blue Mesa at PEFO and the Sonsela Sandstone bed are lithologically

Newark Age APTS Chron (Ma) Petrified Forest 209 E17 ? National Park, AZ

210 52Q-2 210.08±0.22 Ma

211 E16 orest

212 20 meters ified F E15 Member

213 et r P 214 Six Mile GPU Canyon, NM MBb 213.124±0.069 Ma 215 E14 Sonsela Buttes, AZ KWI 216 213.870±0.078 Ma 182Q1 8 20 meters 216.6±0.3 Ma JCWb 214.08±0.20 Ma 7 217 6 Sonsela 5 Sonsela E13 GPL Member

JFb Sandstone bed 4 NORIAN 218 218.017±0.088 Ma SMC 3 SBJ 2

Sonsela Member 218.1±0.7 Ma Wb

L 1 219 E12 219.317±0.068 Ma

CBb ater 220 w Bluewater Creek Member 221 E11 Blu e Creek Member

222 Member E10 Blue Mesa 223 E9 224

225

Figure 3. Stratigraphic sections measured at Petrified Forest National Park, Six Mile Canyon, and the type locality of the Sonsela Sandstone bed with magnetostratigraphy and U-Pb detrital zircon geochronology samples and dates labeled. Detrital zircon samples from the Sonsela Member at the Park labeled GPU, KWI, SBJ, and SMC. CBb—Camp Butte beds; JCWb—Jim Camp Wash beds; JFb—Jasper Forest bed (equivalent to Rainbow Forest bed and Kellogg Butte bed); LWB—Lot’s Wife beds; MBb—Martha’s Butte beds. Adapted from Irmis et al. (2011); U-Pb sample names and dates are from Irmis et al. (2011), Ramezani et al. (2011), and Kent et al. (2018). All dates except that from the Sonsela Buttes are chemical abrasion–thermal ionization mass spectrometry dates. Small numbers next to the section at the Sonsela Buttes reflect the unit numbers of the measured section (Fig. 4). Magnetostratigraphy of the Six Mile Canyon section was accomplished by Zeigler and Geissman (2011) and that of the Petrified Forest National Park section was updated by Zeigler et al. (2017). APTS—astrochronostratigraphic polarity time scale.

identical and stratigraphically equivalent, but disagreed on the correlation Previous U-Pb Detrital Zircon Geochronology of the Sonsela Member with the Rainbow Forest bed, which crops out in the southern portion of PEFO. The Rainbow Forest bed was correlated with either the lower sandstone found The Sonsela Sandstone bed was previously sampled 13.3 km north of at the type locality of the Sonsela Sandstone bed (Cooley, 1957; Heckert and its type section (sample CP20 in Fig. 1) and detrital zircon U-Pb data were Lucas, 2002) or was thought to occur ~6 m above the sandstone capping Blue collected via laser ablation–inductively coupled plasma–mass spectrometry Mesa (Roadifer, 1966). It was also thought to be a distinct sandstone unit that (LA-ICP-MS) (Dickinson and Gehrels, 2008). The data were characterized by a is stratigraphically lower than the equivalent of the Sonsela Sandstone bed significant component of Triassic Cordilleran arc-derived zircon between 227 at PEFO (e.g., Billingsley, 1985; Ash, 1987; Murry, 1990). Ma and 212 Ma, making up 29% of the sample, with three distinct modes in

the spectra of youngest zircon grains at 215 Ma, 218 Ma, and 221 Ma (n = 90; adaptor and a pocket transit compass (Brunton, Inc.). The color of unweathered Dickinson and Gehrels, 2008, 2010). Age-probability plots from LA-ICP-MS rock samples was determined in spot holes using a Munsell rock color chart. data for two samples in the lower part of the Sonsela Member at PEFO were GPS coordinates and photographs of the outcrop were taken using a Garmin determined from an aetosaur quarry in the Jim Camp Wash beds (sample Oregon 550 and Canon EOS Rebel XS digital camera. We collected 5 kg rock 050508-1) and the Long Logs bed (Riggs et al., 2013). Cordilleran arc-derived samples from units 4, 7, and 8 for geochronology from the measured section grains make up 86% and 77% of each sample, respectively, with very minor at the type locality of the Sonsela Sandstone bed (Fig. 3). This fieldwork was age modes throughout the Proterozoic. conducted under a geological reconnaissance permit issued by the Navajo Na- The first high-resolution chemical abrasion–thermal ionization mass spec- tion Minerals Department and the samples are reposited in trust of the Navajo trometry (CA-TIMS) zircon U-Pb dates from the Sonsela Member at PEFO were Nation at the Museum of Northern Arizona in Flagstaff, Arizona. determined by Ramezani et al. (2011) from throughout the member (samples GPL, GPU, KWI, and SBJ in Figs. 1 and 3), yielding 206Pb/238U maximum ages for the maximum depositional age of the top and bottom of the Sonsela LA-ICP-MS Analysis and Data Analysis Member at PEFO of 213.124 ± 0.069 Ma and 219.317 ± 0.080 Ma, respectively. Sample GPL of that study was taken from the Jasper Forest bed and is dated Sample preparation and analysis was performed at the UTChron Geo- at 218.017 ± 0.088 Ma. Thermochronometry Lab at the University of Texas at Austin. The entire sample More recent CA-TIMS zircon U-Pb dates were acquired from a geologic was disaggregated in a jaw crusher and disc mill before hydrodynamic concen- core drilled at Chinde Point (Fig. 1) by the Colorado Plateau Coring Project tration using a Gemini water shaking table. A Franz Isodynamic Separator col- (Olsen et al., 2010, 2018; Kent et al., 2018). The published dates from the core lected the non-magnetic fraction between two heavy mineral separations using sampled similar stratigraphic horizons as the outcrop sampled by Ramezani methyl iodide (2.28 g/mL) and tribromomethane (2.89 g/mL). The zircon crystals et al. (2011) within the upper part of the Sonsela Member at PEFO but without were then mounted via double-sided adhesive tape on an acrylic disc and loaded bed-level correlations in the core, stratigraphic location was only constrained into the large-format two-volume Helex sample cell for LA‑ICP‑MS analysis fol- by core depth. The three relevant CA-TIMS U-Pb dates from the core (Kent lowing the analytical procedures described by Marsh and Stockli (2015). et al., 2018; Olsen et al., 2018) were 214.08 ± 0.20 Ma, 212.81 ± 1.25 Ma, and We randomly selected 122 zircon crystals from the sample taken in the 213.55 ± 0.28 Ma. upper sandstone (unit 8 of the measured section, MNA M.2576). The crystals

Sample Name: 207/235 206/238 207/206 Best age Grain # [U] ppm U/Th 207/235 2σ error 206/238 2σ error RHO Age Ma 2σ error Age (Ma) 2σ error Age (Ma) 2σ error (Ma) 2σ error % Discordance* A sample from the base of what was called the Blue Mesa Member was were ablated with a 30 μm spot size using a PhotonMachines Analyte G.2 dated from Six Mile Canyon near Fort Wingate, New Mexico (Heckert et al., 193 nm Excimer Laser for 30 s at 10 Hz. An Element2 High Resolution ICP-MS 2009, 2012; Irmis et al., 2011), but it is questionable that the Blue Mesa Mem- analyzed 206Pb, 207Pb, 208Pb, 232Th, 235U, and 238U. Analyses were depth-profiled ber is present in New Mexico, and it is more likely that the sampled bed is (time-resolved) in order to monitor for Pb-loss within altered zones of a given situated within the lowest part of the Sonsela Member (see discussion below). zircon. Data reduction was performed using Iolite software with the IgorPro Maximum depositional ages obtained via CA-TIMS for the Six Mile Canyon package (IgorPro, 2015; Paton et al., 2011) and VisualAge data reduction scheme (SMC) bed at Six Mile Canyon (Fig. 3) were determined to be 219.3 ± 3.1 Ma (Petrus and Kamber, 2012). We excluded data from depth-variable intragrain (LA-ICP-MS, Heckert et al., 2009) and 218.1 ± 0.7 Ma (CA-TIMS, Irmis et al., age domains and domains characterized by high common Pb, Pb-loss, or U 2011). An additional date was recovered from the same bed (220.9 ± 0.6 Ma, enrichment (Marsh and Stockli, 2015). The ICP was tuned using the NIST 612 isotope dilution–thermal ionization mass spectrometry (ID-TIMS); Heckert et glass (Jochum et al., 2011). A GJ1 zircon was used as an internal zircon stan- al., 2009, 2012) but the CA-TIMS date (218.1 ± 0.7 Ma; Irmis et al., 2011) is pre- dard (206Pb/238U 601.7 ± 1.3 Ma; Jackson et al., 2004) and was interspersed with ferred because that method provides a more effective treatment for Pb-loss unknown zircon at a 4:1 ratio. An in-house Pak1 zircon was used as a secondary on the outer surface of the zircon and only those data are readily available standard (206Pb/238U 43.03 ± 0.01 Ma). Data were visualized using IsoPlot (Isoplot, for interpretation. 2015). Best ages were selected for each zircon based on careful evaluation of long-term University of Texas laboratory and this study’s data, carefully eval- uating data precision, discordance, and data mode stability. 206Pb/238U ages ■■ METHODS are used for grains <850 Ma and 207Pb/206Pb ages are used for grains >850 Ma, with two-sigma internal error (Gehrels et al., 2008; Horstwood et al., 2016) and 206 238 205 237 1 Supplemental File. Includes U-Pb best age data for Measured Stratigraphic Section discordance assessed between Pb/ U and Pb/ U ages. All analytical and MNA M.2576 and the weighted means calculated methodological details and U-Pb data are in Table S11. All U-Pb Data are also based on 1%, 2%, 3%, and 5% discordance filters. The thickness of each lithological unit at the type section of the Sonsela available from http://www.geochron.org/. Please visit https://doi.org/10.1130/GES02004.S1 or access the full-text article on www.gsapubs.org to Sandstone bed (Akers et al., 1958; Museum of Arizona [MNA] locality 1809) In order to assess the maximum depositional age (MDA) of the upper sand- view the Supplemental File. was measured using a precision Jacob’s staff (ASC Scientific) with compass stone (unit 8) at the type locality of the Sonsela Sandstone bed, we calculated

a weighted mean from the youngest coherent sub-population of detrital zircon with coarse fractions contained in the bottom of fining-upwards sequences. It from the Sonsela sandstone sample. LA-ICP-MS analyses can be more prone to contains planar and trough cross-bedding, chert pebble stringers, and petrified the effects of Pb-loss than ID-TIMS or CA-TIMS, despite pre-analysis ablation wood. The top of the upper sandstone is truncated by erosion, but the unit (<1 micron) to clean the outer surface of each zircon prior to analysis (Gehrels itself is at least 18 m thick. The complete measured section and lithological et al., 2008; Mundil et al., 2008). In order to obtain a robust maximum deposi- descriptions of each unit are found below in Table 1 and can be seen in Figure 4. tional age, all U-Pb data (<240 Ma) were progressively filtered for discordance, ranging from 1%–5% and evaluated for data coherence in terms of mean age and mode. Hence, we applied a 3% discordance filter to select a subset of the U-Pb LA-ICP-MS zircon U-Pb data, based on topology of ranked single grain ages, preserving >50% of the data, and minimizing data characterized by older inheritance and The detrital age spectrum for the sample from the Sonsela Sandstone bed lead loss, to calculate the most robust maximum depositional age for the at its type locality (MNA M.2576) is characterized by a dominant Triassic age Sonsela Sandstone bed. mode (41%) <250 Ma, which is likely derived from the early Mesozoic Cordil- leran magmatic arc (Figs. 5A and 6C; Dickinson and Gehrels, 2008, 2010; Riggs et al., 2013, 2016). Of these Mesozoic zircon crystals, 43 yielded a Norian age ■■ RESULTS (227–208.5 Ma; Cohen et al., 2018; Kent et al., 2017). The next largest detrital age components of the sample are zircons derived from the Yavapai-Mazatzal Stratigraphic Section orogeny and the Archaean craton (each at 13.2%), Grenville orogeny (11.6%), and Mesoproterozoic plutons (10.7%). Detrital zircon associated with the Appa- The type section of the Sonsela Sandstone bed (Akers et al., 1958) crops lachian orogeny, peri-Gondwanan accreted terranes, Paleoproterozoic suture out 5.63 km north of the western Sonsela Butte in Apache County, Arizona. belts, and the Wopmay orogeny each contribute <5% to the sample. (Figs. 1 and 2; Lower Wheatfields, Arizona 7.5 min quadrangle; 36.147298°N, The weighted mean of the 69 Triassic-aged zircon grains with <3% discor- 109.135812°W, datum WGS 84). There, the Bluewater Creek Member of the dance is 216.6 ± 0.3 Ma (mean square weighted deviation [MSWD] = 4.9; Figs. 3, Chinle Formation (units 1–3 of the section measured for this study) underlies 5A, and 6). The distribution of discordance filtered ages shows a dominant the Sonsela Member (units 4–8; Martz and Parker, 2010; Irmis et al., 2011), age mode with younger ages and older ages due to lead loss and inheritance, which contains two prominent sandstones separated by a thin siltstone in- respectively, resulting in an elevated MSWD value. The dominant age group terval (Figs. 2 and 3; Akers et al., 1958). The lower sandstone (unit 4) is 6.5 m exhibits a stable mean age and age mode for different discordance filters thick and is lithologically similar to the upper sandstone. The middle siltstone (1%–5%; Table S1 [footnote 1]) and suggests a robust maximum depositional interval (units 5 and 6) includes layers of greenish shale, greenish gray sandy age of 216.6 ± 0.3 Ma. siltstone, and grayish purple silty claystone. The upper sandstone (units 7 Alternative approaches for determining MDA from a detrital zircon sample and 8) is a well-cemented, well-sorted, quartzose, medium-grained sandstone (Dickinson and Gehrels, 2009) include using the youngest age peak (ca. 218

TABE 1. STRATIGRAPHIC SECTION MEASURED AT THE SONSEA BUTTES, ARIONA, USA Unit Thickness Color Description (m) Unit 8 18.0 Yelloish gray 5Y 8/1 Well-cemented, ell-sorted uartz medium to coarse sandstone. Planar to trough cross-bedding. Chert pebble stringers ith local hite petrified ood. Eroded top surface. Unit 7 3.0 Greenish gray 5G4 6/1 Sharp contact belo ith unit 6. Fine sandstone ith clay and silt fractions. Mostly uartz, micaceous 5, 15–20 black accessory minerals. Unit 6 3.7 Grayish purple 5P 4/2 Silty claystone Unit 5 3.0 Greenish gray 5G4 6/1 Sandy siltstone Unit 4 6.5 Yelloish gray 5Y 8/1 Fine friable sandstone, locally cross-bedded and coarser. uartz, mica, 50 black accessory minerals. Contains thin (cm-scale) beds of smooth, hard greenish shale. Unit 3 5.0 Grayish red purple 5RP 4/2 Slightly silty claystone ith green (5G4 7/4) mottles Unit 2 6.0 Dark reddish bron 10R 3/4 Clayey siltstone ith green (5G4 7/4) mottles Unit 1 6.0 Grayish purple 5P 4/2 Clayey siltstone Total thickness 51.2 N.A. N.A. N.A.not applicable.

240

Mean = 216.57±0.27 Ma MSWD = 4.91 (error bars are 2 σ )

230

Unit 8 220 Unit 7 (Ma) Unit 6

Unit 5 210

Unit 4 200 Units 3 and below

41.3% Units 4 and above Unit 3

Unit 2 y ili t Unit 1 b ob a r p ve Cordilleran arc Cordilleran Archaean craton Archaean Accreted terranes Accreted Grenville orogeny Grenville Wopmay orogeny Wopmay at i Appalachian plutons Appalachian l e Mesoproterozoic plutons Mesoproterozoic Yavapai-Mazatzal orogeny Yavapai-Mazatzal R Paleoproterozoic suture belts suture Paleoproterozoic

1.6% 10.7% 0.8% 11.6% 13.2% 5.8% 1.6% 13.2%

0 500 1000 1500 2000 2500 3000 Best Age (Ma)

Figure 4. Photos of the type section of the Sonsela Sandstone bed showing units of the measured Figure 5. Results of U-Pb detrital zircon laser ablation–inductively coupled plasma–mass spec- stratigraphic section, Arizona, USA. (A) Upper part of the Bluewater Creek Member (units 3 and trometry from the type locality of the Sonsela Sandstone bed, Arizona, USA. (A) Weighted mean below) and Sonsela Sandstone bed (units 4–8). (B) Upper part of the Bluewater Creek Member of Triassic-aged grains from that sample that are <3% discordant (n = 69). (B) Population density (units 1–3) and lower part of the Sonsela Sandstone bed (units 4 and above). Dashed lines indi- curve of type Sonsela Sandstone bed sample (n = 122) with age brackets from Dickinson and cate buried contacts in the photograph. Gehrels (2010). MSWD—mean square weighted deviation.

Ma, Fig. 6B), the youngest single grain (205.8 ± 5.9 Ma), and the weighted mean of the youngest 2σ cluster of grains varying between 206 Ma and 210 Ma, depending on how many grains are used. The youngest age mode is 0.6 3000 fully congruent with the calculated weighted mean of 216.6 ± 0.3 Ma. The youngest single zircon appears to have experienced minor lead loss (Fig. 6) and is incongruent with previous CA-TIMS geochronology established from 2600 the Chinle Formation of northern Arizona, where the youngest MDA is ca. 208

Ma from the Owl Rock Member (Ramezani et al., 2011). The weighted mean U 2200 0.4

age of ca. 217 Ma is also consistent with the lithostratigraphy at the Sonsela 23 8 /

Buttes and previous CA-TIMS geochronology of the upper part of the Petrified b 1800 P

Forest Member at PEFO, which is 212–210 Ma (Riggs et al., 2003; Ramezani et 6 0 al., 2011; Kent et al., 2018). 2 1400

0.2 ■■ DISCUSSION E

The U-Pb zircon maximum depositional age provided here by LA-ICP-MS (216.6 ± 0.3 Ma) for the Sonsela Sandstone bed at the Sonsela Buttes is con- data-point error ellipses are 2σ sistent with the lithostratigraphic correlation of this unit with the Jasper Forest 0.0 0 4 8 12 16 20 24 bed, or more conservatively, with the lower part of the Sonsela Member at 207 235 PEFO (the upper Lot’s Wife beds, Jasper Forest bed, and lowermost Jim Camp Pb/ U Wash beds; Raucci et al., 2006; Martz and Parker, 2010). Three previous U-Pb CA-TIMS dates constrain the age of the Jasper Forest bed at the park, 218.017 y 280 ± 0.088 Ma from the Jasper Forest bed and 213.870 ± 0.088 Ma from the Jim t

0.044 il i e

Camp Wash beds (Fig. 3; samples GPL and KWI, respectively; Ramezani et b

v i a t b al., 2011) and 214.08 ± 0.20 Ma from the Jim Camp Wash beds (Fig. 3; sample a l o e 182Q1; Kent et al., 2018; Olsen et al., 2018) overlap with the date and error of r 260 R p the Sonsela Sandstone bed type section provided here (however, sample GPL 0.040 may be too old for its core depth; Kent et al., 2018). Furthermore, our LA-ICP-MS data places the type Sonsela Sandstone bed squarely within the Norian Stage U 205 215 225 235 240 23 8 (Kent et al., 2017; Cohen et al., 2018). / Best Age (Ma) At PEFO, the Adamanian–Revueltian holochronozone boundary is character- b P

6 0.036

ized by a turnover in the terrestrial biota as observed in phytosaurs, aetosaurs, 0 220 2 and palynomorphs (Parker and Martz, 2011; Reichgelt et al., 2013; Baranyi et al., 2017; Martz and Parker, 2017; Beightol et al., 2018). If vertebrate fossils are found at the type Sonsela Sandstone bed in the future, we hypothesize that 0.032 they would include taxa indicative of the Adamanian land vertebrate estimated 200 holochronozone, such as the non-pseudopalatine leptosuchomorph phytosaur Smilosuchus and the desmatosuchin aetosaurs Scutarx deltatylus and Des- 180 matosuchus smalli (Parker and Martz, 2011; Desojo et al., 2013; Stocker and data-point error ellipses are 2σ 0.028 Butler, 2013; Parker, 2016; Martz and Parker, 2017). 0.19 0.21 0.23 0.25 0.27 0.29 0.31 The Adamanian–Revueltian boundary is hypothesized to coincide strati- 207 235 graphically with a persistent red “silcrete” bed in the lower part of the Jim Pb/ U Camp Wash beds at PEFO that also approximately coincides with evidence of Figure 6. Results of U-Pb detrital zircon laser ablation–inductively coupled plasma–mass spec- increasing aridity in the region (Martz and Parker, 2010; Parker and Martz, 2011; trometry from the type locality (Arizona, USA) of the Sonsela Sandstone bed, continued. (A) U-Pb concordia of all grains in type Sonsela Sandstone bed sample (n = 122). (B) U-Pb concordia of Martz et al., 2012; Atchley et al., 2013). A marked difference in deposition of all Norian-aged grains in the type Sonsela Sandstone bed sample (n = 43). (C) (inset) population the Sonsela Member was reported at this horizon (Howell and Blakey, 2013); density curve of Triassic grains in the type Sonsela Sandstone bed sample.

the lower part of the Sonsela Member (the Camp Butte beds, the Lot’s Wife * CA-TIMS beds, and the Jasper Forest bed) is made up of coarse-grained sheet sands Forest ** ID-TIMS *** LA-ICP-MS that indicate relatively low basin subsidence, and upper part of the Sonsela Forest Member Age Forest Member Member (most of the Jim Camp Wash beds and the Martha’s Butte beds) is (Ma) 215 Member Forest finer-grained with thin sand lenses representing a relatively high rate of basin Sonsela Sonsela Member subsidence. That change in sedimentation is also reflected in the detrital zir- 216 Member Member (~216.6 Ma)*** Sonsela Sonsela con provenance data for the Sonsela Member (Dickinson and Gehrels, 2008, 217 Sandstone bed Member drab mudstone Jasper Forest bed 2010; Riggs et al., 2012, 2013). 218 (218.1 Ma)* (218 Ma)*

The spectral age distribution of MNA M.2576 (Fig. 5B) is nearly identical to NORIAN 219 (219.3 Ma)*** that of sample CP20 from several kilometers north of the type Sonsela Sand- (219.4 Ma)* (220.9 Ma)** (219.4 Ma)* 220 (~220 Ma)* stone bed (Dickinson and Gehrels, 2008, 2010) and samples from the lower drab ember mudstone upper part of the Sonsela Member at PEFO (Riggs et al., 2013). MNA M.2576, CP20, 221 Blue Mesa ember Member eek M

and the Long Logs bed sample included age modes representing grains from r Newspaper Rock bed the Grenville orogeny, Mesoproterozoic plutons, Yavapai-Mazatzal orogeny, Blue Mesa er C eek M and Paleoproterozoic suture belts (Fig. 5B; Dickinson and Gehrels, 2008, 2010). Member r lower er C The sample from the Long Logs bed at PEFO includes age modes from Meso- Blue Mesa Member proterozoic, Yavapai-Mazatzal, and Paleoproterozoic grains, but contains no Blue wa t

zircon from the Grenville orogeny (Riggs et al., 2013). The similarities of the Blue wa t St. Johns, AZ Fort Wingate, NM PEFO, AZ Sonsela Buttes, AZ spectra from MNA M.2576, CP20, and the two samples from the lower part of A A’ the Sonsela Member at PEFO is consistent with the hypothesis that the Son- sela Sandstone bed at its type section correlates to the Jasper Forest bed, or Figure 7. Lithostratigraphic correlations of the Sonsela Member, Blue Mesa Member, and Bluewater Creek Member of the Chinle Formation in Arizona (AZ) and New Mexico (NM), USA. U-Pb dates at least the lower part of the Sonsela Member at PEFO (below the persistent derived from Heckert et al., 2009; Irmis et al., 2011; Ramezani et al., 2011; 2014; and Atchley et al., red “silcrete”), which is dominated by Cordilleran arc-derived zircon (Howell 2013. Chemical abrasion–thermal ionization mass spectrometry (CA-TIMS) dates are designated and Blakey, 2013), rather than the upper part of the Sonsela Member at PEFO. with *, isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates are designated with **, and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) dates The recent CA-TIMS dates for the Chinle Formation (Ramezani et al., 2011, are designated with ***. 2014; Irmis et al., 2011; Atchley et al., 2013; Kent et al., 2018; Olsen et al., 2018) also allow us to begin developing a more sophisticated model of Norian sediment deposition across the Colorado Plateau. The Monitor Butte Member The SMC sample at Six Mile Canyon, New Mexico (ca. 218 Ma), was derived of southern Utah, Cameron Member of northern Arizona, and the Bluewater from a sandstone just below a drab mudstone-dominated unit interpreted by Creek Member of northeastern Arizona and northwestern New Mexico are at previous authors to be correlative to the Blue Mesa Member, immediately least partially correlative with each other (Lucas, 1993; Lucas et al., 1997; Irmis overlying the Bluewater Creek Member (Irmis et al., 2011; also see Heckert and et al., 2011, Kirkland et al., 2014; Martz et al., 2015), and with the lower part Lucas, 2002; Heckert et al., 2009, 2012). Subsequent U-Pb ages older than 219 of the Blue Mesa Member type section at PEFO, with complex interfingering Ma were reported from the type locality of the Bluewater Creek Member in New facies relationships between members occurring across the region (see more Mexico, only a few kilometers from Six Mile Canyon (Ramezani et al., 2014). detailed discussions by Irmis et al., 2011, their supplemental data; Kirkland Moreover, the Placerias Quarry at St. Johns south of PEFO (Fig. 1) occurs in et al., 2014; Martz et al., 2015). In some areas, these units are capped with a a drab-colored mudstone-dominated facies resembling the upper part of the drab mudstone-dominated unit similar to the upper part of the type section of Blue Mesa Member at PEFO (Parker, 2018) with an age of 219.39 Ma (Fig. 7; the Blue Mesa Member at PEFO (Fig. 7; e.g., Lucas et al., 1997; Kirkland et al., Ramezani et al., 2014). These ages suggest that the drab, mudstone-dominated 2014; Martz et al., 2015). The upper drab mudstones have even been assigned “upper Blue Mesa Member” in western New Mexico and in northern Arizona to the Blue Mesa Member (Lucas, 1993; Lucas et al., 1997). Although previous near St. Johns correlates chronostratigraphically with the lowest part of the workers favored lithostratigraphic correlation of these drab mudstones, none Sonsela Member in PEFO (the Lot’s Wife beds; Parker, 2018), rather than with addressed the possibility that the stratigraphic units might be regionally dia- the upper part of the Blue Mesa Member mudstones at PEFO, which ceased chronous, a possibility warranting serious consideration given the striking deposition there at ca. 220 Ma (Ramezani et al., 2011; Atchley et al., 2013). This difference in thickness and complexity between the overlying Sonsela Mem- indicates that the “upper Blue Mesa Member” facies are regionally diachro- ber at PEFO, Sonsela Sandstone bed at the Sonsela Buttes, and potentially nous (Irmis et al., 2011). equivalent Moss Back Member and related sandstones in southern Utah (e.g., It has been hypothesized that the deposition of the Sonsela Member depo- Lucas et al., 1997; Kirkland et al., 2014). sition at PEFO was initiated by a massive alluvial fan that prograded to the

northeast from the Cordilleran magmatic arc during the Norian (Trendell et al., Comments and suggestions from the associate editor and two anonymous reviewers greatly improved the manuscript. This is Petrified Forest National Park Paleontological Contribution No. 2012). A consequence of this model is that the base of the Sonsela Member 59. The conclusions presented here are those of the authors and do not represent the views of should be diachronous, with distal parts of the fan being finer-grained com- the United States Government. pared to coarser and more proximal fan deposits that progressively overlaid them. Here we provide support for diachronous deposition of both fine-grained upper Blue Mesa Member facies and overlying coarse-grained Sonsela Mem- REFERENCES CITED ber facies. Coarse-grained lower Sonsela Member facies at PEFO (the Lot’s Akers, J.P., Cooley, M.E., and Repenning, C.A., 1958, Moenkopi and Chinle formations of Black Mesa and adjacent areas, in Anderson, R.Y., and Harshbarger, J.W., eds., Guidebook of the Wife beds) were being deposited at ca. 218–219 Ma, contemporaneous with Black Mesa Basin, northeastern Arizona: New Mexico Geological Society Guidebook, Ninth finer-grained upper Blue Mesa Member facies to the southeast (St. Johns), Field Conference, p. 88–94, https://ngmdb.usgs.gov/Prodesc/proddesc_90766.htm. west (Zuni Mountains), and north (Navajo Nation); in all three regions, coarse- Ash, S.R., 1987, Petrified Forest National Park, Arizona,in Beus, S.S., ed., Rocky Mountain Section of the Geological Society of America: Centennial Field Guide Volume 2: Boulder, Colorado, grained Sonsela Member facies were deposited later. At least in the Defiance USA, Geological Society of America, p. 405–410, https://doi.org/10.1130/0-8137-5402-X.405. Uplift, the Sonsela Sandstone bed may have been deposited around 214–218 Atchley, S.C., Nordt, L.C., Dworkin, S.I., Ramezani, J., Parker, W.G., Ash, S.R., and Bowring, S.A., Ma (Figs. 3 and 7), about the same time that the lower units within the Sonsela 2013, A linkage among Pangean tectonism, cyclic alluviation, climate change, and biologic turnover in the Late Triassic: The record from the Chinle Formation, southwestern United Member were being deposited in PEFO. States: Journal of Sedimentary Research, v. 83, p. 1147–1161, https://doi.org /10 .2110 /jsr .2013 .89. Baranyi, V., Reichgelt, T., Olsen, P.E., Parker, W.G., and Kürschner, W.M., 2017, Norian vegetation history and related environmental changes: New data from the Chinle Formation, Petri- ■■ fied Forest National Park (Arizona, SW USA): Geological Society of America Bulletin, v. 130, CONCLUSION p. 775–795, https://doi.org/10.1130/B31673.1. Beightol, V.C.V., Parker, W.G., Martz, J.W., and Marsh, A.D., 2018, Estimating the statistical error The interpretation presented here supports the idea that the upper part of observed biostratigraphic ranges within Adamanian-Revueltian vertebrate assemblages of the Late Triassic Chinle Formation of Arizona to test for an abrupt turnover event: [abs.]: So- of the Blue Mesa Member at PEFO is a diachronous siliciclastic transition ciety of Vertebrate Paleontology, 78th Annual Meeting, Meeting Program and Abstracts, p. 88. zone between the micaceous equivalent to the Bluewater Creek Member (the Billingsley, G.H., 1985, General stratigraphy of the Petrified Forest National Park, Arizona: Museum Newspaper Rock bed and lower part of the Blue Mesa Member; Martz and of Northern Arizona Bulletin, v. 54, p. 3–8. Parker, 2010; Ramezani et al., 2014) and the lowest part of the Sonsela Mem- Blakey, R.C., and Gubitosa, R., 1983, Late Triassic paleogeography and depositional history of the Chinle Formation, southern Utah and northern Arizona, in Reynolds, M.W., and Dolly, E.D., eds., ber (Fig. 7). Future analyses should target the Sonsela Member–Blue Mesa Mesozoic Paleogeography of the West-Central United States: Rocky Mountain Section, Sympo- Member transition zone and the rest of the Sonsela Member and its partial sium 2, Denver, Colorado, USA, Society of Economic Paleontologists and Mineralogists, p. 57–76. equivalents in Utah (such as the Moss Back Member) using high-resolution Cohen, K.M., Harper, D.A.T., and Gibbard, P.L., 2018, ICS International Chronostratigraphic Chart version 2018/08: International Commission on Stratigraphy, International Union of Geological CA-TIMS to improve age precision and resolution of the youngest mode of Sciences, www.stratigraphy.org (last accessed September 2018). detrital zircon U-Pb data to refine cross-state correlations of the members Cooley, M.E., 1957, Geology of the Chinle Formation in the upper Little Colorado drainage area, of the Chinle Formation that preserve the rock record of the Adamanian–Re- Arizona and New Mexico [M.S. thesis]: Tucson, Arizona, USA, University of Arizona, 317 p. Desojo, J.B., Heckert, A.B., Martz, J.W., Parker, W.G., Schoch, R.R., Small, B.J., and Sulej, T., 2013, vueltian boundary. Our LA-ICP-MS U-Pb data support the hypothesis that the Aetosauria: A clade of armoured pseudosuchians from the Upper Triassic continental beds, in uppermost Blue Mesa Member and the Sonsela Member (and the Sonsela Nesbitt, S.J., Desojo, J.B., and Irmis, R.B., eds., Anatomy, Phylogeny and Palaeobiology of Early Sandstone bed at its type locality) were deposited in a continental backarc Archosaur and their Kin: Geological Society of London Special Publication 379, p. 203–239, https://doi.org/10.1144/SP379.17. basin (Howell and Blakey, 2013) or retroarc foreland basin (Riggs et al., 2016) Dickinson, W.R., and Gehrels, G.E., 2008, U-Pb ages of detrital zircon in relation to paleogeography: by a large “megafan” prograding from the southwest into the northwesterly Triassic paleodrainage networks and sediment dispersal across southwest Laurentia: Journal flowing Chinle stem fluvial system (Riggs et al., 2012, 2013). Finally, our data of Sedimentary Research, v. 78, p. 745–764, https://doi.org/10.2110/jsr.2008.088. Dickinson, W.R., and Gehrels, G.E., 2009, Use of U-Pb ages of detrital zircons to infer maximum provide another example of how U-Pb geochronology can clarify stratigraphic depositional ages of strata: A test against a Colorado Plateau database: Earth and Planetary relationships and the diachroneity of fluvial depositional systems, as well as Science Letters, v. 288, p. 115–125, https://doi.org/10.1016/j.epsl.2009.09.013. their influences on regional biostratigraphy. Dickinson, W.R., and Gehrels, G.E., 2010, Insights into North American paleogeography and paleotectonics from U-Pb ages of detrital zircon in Mesozoic strata of the Colorado Plateau, USA: International Journal of Earth Sciences, v. 99, p. 1247–1265, https://doi .org/10.1007 /s00531-009-0462-0. ACKNOWLEDGMENTS Dubiel, R.F., and Hasiotis, S.T., 2011, Deposystems, paleosols, and climatic variability in a continen- We thank Jake Tapaha, an intern at PEFO in 2012, for help measuring the section described in tal system: The Upper Triassic Chinle Formation, Colorado Plateau, U.S.A., in Davidson, S.K., this paper. Fieldwork on the Navajo Nation was conducted under permits from the Navajo Nation and Leleu, S., and North, C.P., eds., From River to Rock Record: The Preservation of Fluvial Minerals Department issued by Mr. Ahktar Zaman and Mr. Brad Nesemeier. Any persons wishing Sediments and their Subsequent Interpretation: SEPM (Society for Sedimentary Geology) to conduct geologic investigations on the Navajo Nation must first apply for and receive a per- Special Publication 97, p. 393–421, https://doi.org/10.2110/sepmsp.097.393. mit from, P.O. Box 1910, Window Rock, Arizona 86515 and telephone number (928) 871–6587. We Gehrels, G.E., Valencia, V.A., and Ruiz, J., 2008, Enhanced precision, accuracy, efficiency, and also thank Lisa Stockli and the graduate students at the UTChron Laboratory at the University spatial resolution of U-Pb ages by laser ablation–multicollector–inductively coupled plasma– of Texas at Austin analytical assistance and constructive discussions. We thank Timothy Rowe, mass spectrometry: Geochemistry, Geophysics, Geosystems, v. 9, p. 1–13, https://doi .org/10 Christopher Bell, Julia Clarke, and Hans-Dieter Sues for reviewing an early draft of this manuscript. .1029/2007GC001805.

Gregory, H.E., 1917, Geology of the Navajo country; a reconnaissance of parts of Arizona, New Lucas, S.G., 1993, The Chinle Group: Revised stratigraphy and biochronology of Upper Triassic Mexico, and Utah: U.S. Geological Survey Professional Paper 93, 161 p., https://doi .org /10 nonmarine strata in the western United States, in Morales, M., ed., Aspects of Mesozoic Geology .3133/pp93. and Paleontology of the Colorado Plateau: Museum of Northern Arizona Bulletin, v. 59, p. 27–50. Gregory, H.E., 1950, Geology and geography of the Zion Park region, Utah and Arizona: U.S. Geo- Lucas, S.G., Heckert, A.B., Estep, J.W., and Anderson, O.J., 1997, Stratigraphy of the Upper Trias- logical Survey Professional Paper 220, 200 p., https://doi.org/10.3133/pp220. sic Chinle Group, Four Corners Region, in Anderson, O.J., Kues, B.S., and Lucas, S.G., eds., Harshbarger, J.W., Repenning, C.A., and Irwin, J.H., 1957, Stratigraphy of the uppermost Triassic Mesozoic Geology and Paleontology of the Four Corners Region: Albuquerque, New Mexico, and Jurassic rocks of the Navajo Country: U.S. Geological Survey Professional Paper 291, 73 p. USA, New Mexico Geological Society Guidebook, v. 48, p. 81–107. Heckert, A.B., and Lucas, S.G., 2002, Revised Upper Triassic stratigraphy of the Petrified Forest Na- Marsh, J.H., and Stockli, D.F., 2015, Zircon U-Pb and trace element zoning characteristics in an ana- tional Park, Arizona, U.S.A., in Heckert, A.B, and Lucas, S.G., eds., Upper Triassic Stratigraphy tectic granulite domain: Insights from LASS-ICP-MS depth profiling: Lithos, v. 239, p. 170–185, and Paleontology: New Mexico Museum of Natural History and Science Bulletin, v. 21, p. 37–42. https://doi.org/10.1016/j.lithos.2015.10.017. Heckert, A.B., Lucas, S.G., Dickinson, W.R., and Mortensen, J.K., 2009, New ID-TIMS U-Pb ages for Martz, J.W., and Parker, W.G., 2010, Revised lithostratigraphy of the Sonsela Member (Chinle Chinle Group strata (Upper Triassic) in New Mexico and Arizona, correlation to the Newark Super- Formation, Upper Triassic) in the southern part of Petrified Forest National Park, Arizona: group, and implications for the “long Norian.”: Geological Society of America Abstracts with Pro- PLoS One, v. 5, https://doi.org/10.1371/journal.pone.0009329. grams, v. 41, no. 7, p. 123, http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_162342.htm. Martz, J.W., and Parker, W.G., 2017, Revised formation of the Late Triassic Land Vertebrate “Fau- Heckert, A.B., Lucas, S.G., and Spielmann, J.A., 2012, A new species of the enigmatic archosauro nachrons” of western North America: Recommendations for codifying nascent systems of morph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA: vertebrate biochronology, in Zeigler, K.E., and Parker, W.G., eds., Terrestrial Depositional Palaeontology, v. 55, p. 1333–1348, https://doi.org/10.1111/j.1475-4983.2012.01200.x. Systems: Deciphering Complexities Through Multiple Stratigraphic Methods: Amsterdam, Horstwood, M.S.A., Kosler, J., Gehrels, G., Jackson, S.E., McLean, N.M., Paton, C., Pearson, N.J., The Netherlands, Elsevier, p. 39–125, https://doi.org/10.1016/B978-0-12-803243-5.00002-9. Sircombe, K., Sylvester, P., Vermeesch, P., Bowring, J.F., Condon, D.J., and Schoene, B., 2016, Martz, J.W., Parker, W.G., Skinner, L., Raucci, J.J., Umhoefer, P., and Blakey, R.C., 2012, Geologic Community-derived standards for LA-ICP-MS U-(Th-)Pb geochronology- uncertainty propaga- map of Petrified Forest National Park, Arizona: Arizona Geological Survey Contributed Map tion, age interpretation and data reporting: Geostandards and Geoanalytical Research, v. 40, CM-12-A, 1 map sheet, scale 1:50,000, 18 p., http://repository.azgs.az.gov/uri_gin/azgs/dlio/1487. p. 311–332, https://doi.org/10.1111/j.1751-908X.2016.00379.x. Martz, J.W., Kirkland, J.I., DeBlieux, D.D., Suarez, C.A., and Santucci, V.L., 2015, Stratigraphy of the Howell, E.R., and Blakey, R.C., 2013, Sedimentological constraints on the evolution of the Cor- Chinle Formation (Upper Triassic) and Moenave Formation (Upper Triassic-Lower Jurassic) in dilleran arc: New insights from the Sonsela Member, Upper Triassic Chinle Formation, Pet- the southwestern part of Zion National Park, Washington County, Utah: Unpublished Open rified Forest National Park (Arizona, USA): Geological Society of America Bulletin, v. 125, File Report, Utah Geological Survey, 104 p. p. 1349–1368, https://doi.org/10.1130/B30714.1. McKee, E.D., 1937, Triassic pebbles in northern Arizona containing invertebrate fossils: American IgorPro, 2015, Technical graphing and data analysis software for scientists and engineers: https:// Journal of Science, v. 33, p. 260–263, https://doi.org/10.2475/ajs.s5-33.196.260. www.wavemetrics.com/products/igorpro/igorpro.htm (last accessed January 2016). Mundil, R., Gehrels, G., Deino, A.L., and Irmis, R.B., 2008, Zircon U-Pb analyses by TIMS and Ingersoll, R.V., 2012, Tectonics of sedimentary basins, with revised nomenclature, in Busby, C., LA‑ICPMS on the same material: Eos (Transactions, American Geophysical Union), v. 89 (Fall and Azor Perez, A., eds., Tectonics of Sedimentary Basins: Recent Advances: Hoboken, New Meeting Supplement), V13A-2108. Jersey, USA, Blackwell Publishing Ltd., p. 3–43. Murry, P.A., 1990, Stratigraphy of the Upper Triassic Petrified Forest Member (Chinle Formation) Irmis, R.B., Mundil, R., Martz, J.W., and Parker, W.G., 2011, High-resolution U-Pb ages from the in Petrified Forest National Park, Arizona, USA: The Journal of Geology, v. 98, p. 780–789, Upper Triassic Chinle Formation (New Mexico, USA) support a diachronous rise of dinosaurs: https://doi.org/10.1086/629441. Earth and Planetary Science Letters, v. 309, p. 258–267, https://doi .org /10 .1016 /j .epsl .2011 .07 .015. North American Commission on Stratigraphic Nomenclature, 2005, North American Stratigraphic Isoplot, 2015, A flexible tool for the mathematical and graphical interpretation of radiogenic-isotope Code: American Association of Petroleum Geoscientists Bulletin, v. 89, p. 1547–1591, https:// data: http://www.bgc.org/isoplot_etc/isoplot.html (last accessed January 2016). doi.org/10.1306/07050504129. Jackson, S.E., Pearson, N.J., Griffin, W.L., and Belousova, E.A., 2004, The application of laser ab- Olsen, P.E., Kent, D.V., Geissman, J.W., Bachmann, G., Blakey, R.C., and Sha, J.G., 2010, The Colo- lation-inductively coupled plasma-mass spectrometry to in situ U-Pb zircon geochronology: rado Plateau Coring Project (CPCP): 100 million years of Earth system history: Earth Science Chemical Geology, v. 211, p. 47–69, https://doi.org/10.1016/j.chemgeo.2004.06.017. Frontiers, v. 17, p. 55–63, https://doi.org/10.7916/D86Q1V70. Jochum, K.P., Weis, U., Stoll, B., Kuzmin, D., Yang, Q., Raczek, I., Jacob, D.E., Stracke, A., Birbaum, Olsen, P.E., Geissman, J.W., Kent, D.V., Gehrels, G.E., Mundil, R., Irmis, R.B., Lepre, C., Rasmussen, K., Frick, D.A., Günther, D., and Enzweiler, J., 2011, Determination of reference values for NIST C., Giesler, D., Parker, W.G., Zakharova, N., Kürschner, W.M., Miller, C., Baranyi, V., Schaller, SRM 610-617 glasses following ISO guidelines: Geostandards and Geoanalytical Research, M.F., Whiteside, J.H., Schnurrenberger, D., Noren, A., Shannon, K.B., O’Grady, R., Colbert, v. 35, p. 397–429, https://doi.org/10.1111/j.1751-908X.2011.00120.x. M.W., Maisano, J., Edey, D., Kinney, S.T., Molina-Garza, R., Bachman, G.H., and Sha, J., 2018, Kent, D.V., Olsen, P.E., and Muttoni, G., 2017, Astrochronostratigraphic polarity time scale (APTS) Colorado Plateau Coring Project, Phase I (CPCP-I): A continuously cored, globally exportable for the Late Triassic and Early Jurassic from continental sediments and correlation with chronology of Triassic continental environmental change from western North America: Sci- standard marine stages: Earth-Science Reviews, v. 166, p. 153–180, https://doi .org/10.1016 entific Drilling, v. 24, p. 15–40, https://doi.org/10.5194/sd-24-15-2018. /j.earscirev.2016.12.014. Parker, W.G., 2016, Revised phylogenetic analysis of the Aetosauria (Archosauria: Pseudosuchia): Kent, D.V., Olsen, P.E., Rasmussen, C., Lepre, C., Mundil, R., Irmis, R.B., Gehrels, G.E., Giesler, D., Assessing the effect of incongruent morphological character sets: PeerJ, v. 4, e1583, https:// Geissman, J.W., and Parker, W.G., 2018, Empirical evidence for stability of the 405-kiloyear doi.org/10.7717/peerj.1583. Jupiter-Venus eccentricity cycle over hundreds of millions of years: Proceedings of the Na- Parker, W.G., 2018, Redescription of Calyptosuchus (Stagonolepis) wellesi (Archosauria: Pseudo- tional Academy of Sciences of the United States of America, v. 115, p. 6153–6158, https://doi suchia: Aetosauria) from the Late Triassic of the Southwestern United States with a discussion .org/10.1073/pnas.1800891115. of genera in vertebrate paleontology: PeerJ, v. 6, e4291, https://doi.org/10.7717/peerj.4291. Kiersch, G.A., 1955, Mineral Resources, Navajo-Hopi Indiana Reservations, Arizona-Utah: Nonme- Parker, W.G., and Martz, J.W., 2011, The Late Triassic (Norian) Adamanian–Revueltian tetrapod tallic Minerals: Geology, Evaluation, and Uses, Volume 2: Tucson, Arizona, USA, University faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona: Earth and of Arizona Press, 75 p. Environmental Science Transactions of the Royal Society of Edinburgh, v. 101, p. 231–260, Kirkland, J.I., Martz, J.W., DeBlieux, D.D., Santucci, V.L., Madsen, S.K., and Wood, J.R., 2014, Pale- https://doi.org/10.1017/S1755691011020020. ontology resource inventory and monitoring, Chinle and Cedar Mountain formations, Capitol Parker, W.G., and Martz, J.W., 2017, Building local biostratigraphic models for the Upper Triassic Reef National Park, Utah: Unpublished Open File Report, Utah Geological Survey, 123 p. of western North America: Methods and considerations, in Zeigler, K.E., and Parker, W.G., Kuhlemann, J., and Kempf, O., 2002, Post-Eocene evolution of the North Alpine foreland basin eds., Terrestrial Depositional Systems: Deciphering Complexities Through Multiple Strati- and its response to Alpine tectonics: Sedimentary Geology, v. 152, p. 45–78, https://doi .org graphic Methods: Amsterdam, The Netherlands, Elsevier, p. 1–38, https://doi.org/10.1016 /10.1016/S0037-0738(01)00285-8. /B978-0-12-803243-5.00001-7.

Paton, C., Hellstrom, J.C., Bence, P., Woodhead, J.D., and Hergt, J.M., 2011, Iolite: Freeware for Riggs, N.R., Oberling, Z.A., Howell, E.R., Parker, W.G., Barth, A.P., Cecil, M.R., and Martz, J.W., the visualization and processing of mass spectrometric data: Journal of Analytical Atomic 2016, Sources of volcanic detritus in the basal Chinle Formation, southwestern Laurentia, Spectrometry, v. 26, p. 2508–2518, https://doi.org/10.1039/c1ja10172b. and implications for the Early Mesozoic magmatic arc: Geosphere, v. 12, p. 439–463, https:// Petrus, J.A., and Kamber, B.S., 2012, VizualAge: A novel approach to laser ablation ICP-MS U-Pb doi.org/10.1130/GES01238.1. geochronology data reduction: Geostandards and Geoanalytical Research, v. 36, p. 247–270, Roadifer, J.E., 1966, Stratigraphy of the Petrified Forest National Park, Arizona [Ph.D. thesis]: https://doi.org/10.1111/j.1751-908X.2012.00158.x. Tucson, Arizona, USA, University of Arizona, 152 p. Ramezani, J., Hoke, G.D., Fastovsky, D.E., Bowring, S.A., Therrien, F., Dworkin, S.I., Atchley, S.C., Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, Stratigraphy and origin of the Chinle Formation and Nordt, L.C., 2011, High-precision U-Pb zircon geochronology of the Late Triassic Chinle and related Upper Triassic strata in the Colorado Plateau region: U.S. Geological Survey Formation, Petrified Forest National Park (Arizona, USA): Temporal constraints on the early Professional Paper 690, 336 p., https://doi.org/10.3133/pp690. evolution of dinosaurs: Geological Society of America Bulletin, v. 123, p. 2142–2159, https:// Stocker, M.R., and Butler, R.J., 2013, Phytosauria, in Nesbitt, S.J., Desojo, J.B., and Irmis, R.B., doi.org/10.1130/B30433.1. eds., Anatomy, Phylogeny and Palaeobiology of Early Archosaur and their Kin: Geological Ramezani, J., Fastovsky, D.E., and Bowring, S.A., 2014, Revised chronostratigraphy of the lower Society of London Special Publication 379, p. 91–117. Chinle Formation strata in Arizona and New Mexico (USA): High-precision U-Pb geochrono- Trendell, A.M., Atchley, S.C., and Nordt, L.C., 2012, Depositional and diagenetic controls on reser- logical constraints on the Late Triassic evolution of dinosaurs: American Journal of Science, voir attributes within a fluvial outcrop analog, Upper Triassic Sonsela Member of the Chinle v. 314, p. 981–1008, https://doi.org/10.2475/06.2014.01. Formation, Petrified Forest National Park, Arizona: AAPG Bulletin, v. 96, p. 679–707, https:// Raucci, J.J., Blakey, R.C., and Umhoefer, P.J., 2006, A new geologic map of Petrified Forest National doi.org/10.1306/08101111025. Park with emphasis on members and key beds of the Chinle Formation, in Parker, W.G., Ash, Weissmann, G.S., Hartley, A.J., Nichols, G.J., Scuderi, L.A., Olsen, M., Buehler, H., and Banteah, S.R., and Irmis, R.B., eds., A Century of Research at Petrified Forest National Park 1906–2006: R., 2010, Fluvial form in modern continental sedimentary basins: Distributive fluvial systems: Museum of Northern Arizona Bulletin, v. 62, p. 157–159. Geology, v. 38, p. 39–42, https://doi.org/10.1130/G30242.1. Reichgelt, T., Parker, W.G., Martz, J.W., Conran, J.G., Van Konijnenburg-Van Cittert, J.H., and Weissmann, G.S., Hartley, A.J., Scuderi, L.A., Nichols, G.J., Owen, A., Wright, S., Felicia, A.L., Kürschner, W.M., 2013, The palynology of the Sonsela member (Late Triassic, Norian) at Holland, F., and Anaya, F.M.L., 2015, Fluvial geomorphic elements in modern sedimentary Petrified Forest National Park, Arizona, USA: Review of Palaeobotany and Palynology, v. 189, basins and their potential preservation in the rock record: A review: Geomorphology, v. 250, p. 18–28, https://doi.org/10.1016/j.revpalbo.2012.11.001. p. 187–219, https://doi.org/10.1016/j.geomorph.2015.09.005. Repenning, C.A., Cooley, M.E., and Akers, J.P., 1969, Stratigraphy of the Chinle and Moenkopi Woody, D.T., 2003, Revised geological assessment of the Sonsela Member, Chinle Formation, formations, Navajo and Hopi Indian reservations, Arizona, New Mexico, and Utah: U.S. Geo- Petrified Forest National Park, Arizona [M.S. thesis]: Flagstaff, Arizona, USA, Northern Ari- logical Survey Professional Paper 521-B, 34 p., https://doi.org/10.3133/pp521B. zona University, 206 p. Riggs, N.R., Ash, S.R., Gehrels, G.E., and Wooden, J.L., 2003, Isotopic age of the Black Forest Bed, Pet- Woody, D.T., 2006, Revised stratigraphy of the Lower Chinle Formation (Upper Triassic) of Petrified rified Forest Member, Chinle Formation, Arizona: An example of dating a continental sandstone: Forest National Park, Arizona, in Parker, W.G., Ash, S.R., and Irmis, R.B., eds., A Century of Geological Society of America Bulletin, v. 115, p. 1315–1323, https://doi .org /10 .1130 /GES00860 .1. Research at Petrified Forest National Park 1906–2006: Museum of Northern Arizona Bulletin, Riggs, N.R., Barth, A.P., Gonzalez-Leon, C.M., Jacobson, C.E., Wooden, J.L., Howell, E.R., and v. 62, p. 17–45. Walker, J.D., 2012, Provenance of Upper Triassic strata in southwestern North America as Zeigler, K.E., and Geissman, J.W., 2011, Magnetostratigraphy of the Upper Triassic Chinle Group suggested by isotopic analysis and chemistry of zircon crystals, in Rasbury, E.T., Hemming, of New Mexico: Implications for regional and global correlations among Upper Triassic se- S.R., and Riggs, N.R., eds., Mineralogical and Geochemical Approaches to Provenance: Geo- quences: Geosphere, v. 7, p. 802–829, https://doi.org/10.1130/GES00628.1. logical Society of America Special Paper 487, p. 13–36, https://doi.org/10.1130/2012.2487(02). Zeigler, K.E., Parker, W.G., and Martz, J.W., 2017, The lower Chinle Formation (Late Triassic) at Riggs, N.R., Reynolds, S.J., Lindner, P.J., Howell, E.R., Barth, A.P., Parker, W.G., and Walker, J.D., Petrified Forest National Park, southwestern USA: A case study in magnetostratigraphic cor- 2013, The Early Mesozoic Cordilleran arc and Late Triassic paleotopography: The detrital re- relations, in Ziegler, K.E., and Parker, W.G., eds., Terrestrial Depositional Systems: Deciphering cord in Upper Triassic sedimentary successions on and off the Colorado Plateau: Geosphere, Complexities Through Multiple Stratigraphic Methods: Amsterdam, The Netherlands, Elsevier, v. 9, p. 602–613, https://doi.org/10.1130/GES00860.1. p. 237–277, https://doi.org/10.1016/B978-0-12-803243-5.00006-6.