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Maximum depositional age and provenance of the Uinta Mountain Group and Big Cottonwood Formation, northern Utah: Paleogeography of rifting western Laurentia

Carol M. Dehler, C. Mark Fanning, Paul K. Link, Esther M. Kingsbury and Dan Rybczynski

Geological Society of America Bulletin published online 20 May 2010; doi: 10.1130/B30094.1

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Copyright © 2010 Geological Society of America Published online May 20, 2010; doi:10.1130/B30094.1 Downloaded from gsabulletin.gsapubs.org on May 29, 2010

Maximum depositional age and provenance of the Uinta Mountain Group and Big Cottonwood Formation, northern Utah: Paleogeography of rifting western Laurentia

Carol M. Dehler1,†, C. Mark Fanning2, Paul K. Link3, Esther M. Kingsbury3, and Dan Rybczynski1 1Department of Geology, Utah State University, Logan, Utah 84322, USA 2Research School of Earth Sciences, Australian National University, Canberra 0200, Australia 3Department of Geosciences, Idaho State University, Pocatello, Idaho 83209, USA

ABSTRACT ming province); 1.6–1.8 Ga (Paleoprotero- tuffaceous beds or microfossils with calibrated zoic Yavapai province); 1.5–1.6 Ga (Early short stratigraphic ranges. U-Pb detrital zircon analyses provide a Mesoproterozoic North American mag- The application of detrital zircon U-Pb geo- new maximum depositional age constraint matic gap), 1.4–1.45 Ga (Colorado province chronology has signifi cantly advanced Protero- on the Uinta Mountain Group (UMG) and A-type granite-rhyolite belt); 0.93–1.2 Ga zoic sedimentologic and stratigraphic research. correlative Big Cottonwood Formation (eastern Grenvillian orogen); and mid- Maximum depositional ages obtained from the (BCF) of Utah, and signifi cantly enhance our Neoproterozoic volcanic grains (766 Ma). youngest zircon age populations are now known insights on the mid-Neoproterozoic paleo- Sediment was transported by: (1) a major for Proterozoic basins on many continents (e.g., geographic and tectonic setting of western longitudinal west-fl owing river system tap- Ross et al., 1992; Rainbird et al., 1997; Evans Laurentia. A sandstone interval of the Out- ping the Grenville orogen, (2) local south- et al., 2000; Southgate et al., 2000; Smithies et al., law Trail formation with a youngest popu- fl owing drainages off the southern Wyoming 2001; Goodge et al., 2002; Ross and Villeneuve, lation (n = 4) of detrital zircons, from a craton, and (3) northerly and westerly 2003; Jackson et al., 2005; Maclean et al., 2006; sampling of 128 detrital zircon grains, yields fl owing marine currents. The Uinta Moun- Cawood et al., 2007; Cross and Crispe, 2007; a concordia age of 766 ± 5 Ma. This defi nes a tain Group river system was one of several Link et al., 2007; Amato et al., 2008), although maximum age for deposition of the lower- major transcontinental drainages that deliv- they do not always yield an age that represents middle Uinta Mountain Group in the east- ered Grenvillian zircon grains to the proto– the timing of deposition. Detrital zircon U-Pb ern Uinta Mountains and indicates that Pacifi c Ocean. We propose that this river age populations also provide fundamental prov- the group is no older than middle Neo- system ultimately supplied sediment to peri- enance information toward understanding the proterozoic in age (i.e., Cryogenian). These Gondwanan margins along the proto-Pacifi c paleogeographic development of Laurentia’s data support a long-proposed correlation to Antarctica, Australia, and South America, Proterozoic rift margins, although data are lim- with the Chuar Group of Grand Canyon providing an alternative source for explain- ited for middle Neoproterozoic Laurentia (Rain- (youngest age 742 Ma ± 6 Ma), which, like ing the problematic provenance of Grenvil- bird et al., 1997; Stewart et al., 2001; Cawood the Uinta Mountain Group and Big Cotton- lian grains in these areas. et al., 2007). wood Formation, records nonmagmatic in- Provenance interpretations of the Uinta tracratonic extension. This suggests a ~742 INTRODUCTION Mountain Group and Big Cottonwood Forma- to ≤766 Ma extensional phase in Utah and tion, based on sedimentologic, petrographic, Arizona that preceded the regional rift epi- Geochronologic constraints on Neoprotero- geochemical, and Nd-isotope data, support sode (~670–720 Ma), which led to develop- zoic successions are imperative for under- a general model of quartz sand derived from ment of the Cordilleran passive margin. standing the geologic history of the western eastern Proterozoic and distal Archean sources This is likely an intracratonic response to an Laurentian margin in its Rodinian and wider and feldspathic sand derived from proximal early rift phase of Rodinia. Further, because context. The Neoproterozoic Uinta Mountain Archean sources to the north (Wallace, 1972; the Chuar Group and the Uinta Mountain Group (UMG) and correlative Big Cotton- Sanderson, 1984; Ball and Farmer, 1998; Group–Big Cottonwood Formation strata wood Formation (BCF) of northern Utah form Condie et al., 2001). Preliminary detrital zircon record intracratonic marine deposition, this a signifi cant part of this margin. These strata U-Pb and Hf data (n = 4 samples) generated correlation suggests a regional ~740–770 Ma are included in Succession B of North America from the Uinta Mountain Group show a domi- transgression onto western Laurentia. (>720 to <1000 Ma), which is hypothesized to nant Mesoprotero zoic (1.1 Ga–Grenvillian) The detrital grain-age distributions from record intracratonic basin development mark- age population with Hf isotope values sug- 12 samples include the following grain-age ing the early stages of the breakup of Rodinia gesting derivation from enriched Grenvillian populations and interpreted provenance: (Stewart, 1972; Young et al., 1979, 1981; Rain- basement now in the subsurface of south- 2.5–2.7 Ga (late Archean southern Wyo- bird et al., 1996, 1997). Until this study, these eastern North America (Mueller et al., 2007). km-thick successions have lacked geochrono- Prior to this study, Paleo protero zoic and mid- †E-mail: [email protected] logic control because they contain no known Neoproterozoic detrital zircon ages had not

GSA Bulletin; September/October 2010; v. 122; no. 9/10; p. 1686–1699; doi: 10.1130/B30094.1; 7 fi gures; 1 table; Data Repository item 2010129.

1686 For permission to copy, contact [email protected] © 2010 Geological Society of America Downloaded from gsabulletin.gsapubs.org on May 29, 2010 Maximum depositional age and provenance of the Uinta Mountain Group and Big Cottonwood Formation, northern Utah been reported from the Uinta Mountain Group, fault system 3 and no detrital zircons had been analyzed from A North Flank the Big Cotton wood Formation. Salt Lake City 10 Uinta Anticline 5 4 Browns Park In this paper, we present new SHRIMP 11 8,9 (sensitive high-resolution microprobe) detri- 2 6 7

tal zircon U-Pb data for 12 samples from the CO 1 12 UT Uinta Mountain Group and the Big Cotton- Uinta Mountain Group wood Formation, along with stratigraphic Big Cottonwood Fm. Vernal and sedimentologic data collected in the past decade (Figs. 1 and 2; Table 1) (Ehlers 50° 110° 105° and Chan, 1999; De Grey and Dehler, 2005; B 100° 95° Brehm, 2007; Brehm, 2008; Kingsbury, 2008; Medicine Hat CANADA USA Rybczynski, 2009). We hypothesize that the (2.6–3.3 Ga) MT ND Uinta Mountain Group and Big Cottonwood Trans-Hudson Superior Formation intracratonic basin can be placed Great Falls Orogen Craton into a mid-Neoproterozoic context (i.e., Cryo- tectonic zone (>2.5 Ga) (1.86–1.77 Ga) (3.2–2.5 Ga, genian [850–635 Ma], Plumb, 1991; Knoll Selway 1.92–1.77 Ga) et al., 2004; U.S. Geological Survey Geologic (2.4–1.6 Ga) Names Committee, 2006). We also test corre- SD lations within Succession B strata in western 45° North America, as well as extracontinental Wyoming WY To Grenville correlations, thus providing a refi ned view of ID Craton Orogen and the paleogeographic and tectonic setting of the foreland Uinta Mountain Group–Big Cottonwood For- Grouse (>2.5 Ga) Creek Belt NE mation basin and surrounding region. Central (>2.5 Ga) Plains REGIONAL PRECAMBRIAN GEOLOGY UT Cheyenne (1.8–1.7 Ga)

Uinta Mountain Group Farmington Zone Farmington

40° The Uinta Mountain Group of north-central Yavapai Utah is a thick siliciclastic succession that Interior Mojave (1.8–1.7 Ga) crops out in the east-west–trending Uinta (2.0–1.7 Ga) N Mountains, east of Salt Lake City (Fig. 1A). seaway CO 200 km There, the UMG is a 4-km-thick succession of cross-bedded orthoquartzite and sandstone, Figure 1. (A) Inset showing the outcrop extent of the Neoproterozoic units sampled in this siltstone, and shale; it has no exposed base study. Green stars with numbers 1 through 12 indicate sample locations from this study and and is unconformably overlain by Paleozoic are keyed to Figures 2A and 3 and Table DR1 [see footnote 1]. Blue dots are sample loca- strata (Fig. 2A). It is subdivided into six for- tions of Mueller et al. (2007). 1 and 2—Big Cottonwood Formation; 3—Jesse Ewing Canyon mations, four of them informal, and is inter- Formation; 4—Outlaw Trail formation; 5—Red Castle formation; 6—Moosehorn Lake preted to record fl uvial and marine deposition formation; 7—Mount Watson Formation; 8—Deadhorse Pass formation; 9 and 10—Hades (Fig. 2A and Table 1) (e.g., Wallace, 1972; Pass quartzite; and 11 and 12—Red Pine Shale. (B) Paleogeographic reconstruction of the Sanderson, 1984). The lower Red Castle for- Uinta Mountain and Big Cottonwood basin at ~742 to <770 Ma showing possible source mation and much of the Hades Pass quartzite areas for arkosic and quartz-rich sediment and hypothesized extent of intracratonic seaway indicate transverse fl uvial and deltaic systems (transgression shown in blue). Larger arrows indicate paleofl ow of major fl uvial systems. fl owing southward (Table 1; Wallace , 1972; Medium-sized arrows show paleofl ow of transverse drainages. Smallest arrows show paleo- Kingsbury, 2008). All other units in the west- fl ow of longshore and tidal currents. Red arrows indicate modifi cation to previous models ern Uinta Mountain Group are largely marine (black arrows). See text for further comparison with previous models. (Base map modifi ed siliciclastic shelf deposits that were infl uenced from Foster et al., 2006.) by west-fl owing longshore currents, west- ward- and southward-prograding deltas, and northerly directed tidal currents (Fig. 2A and Paleoprotero zoic Red Creek Quartzite and is et al., 2007). The overlying ~6+ km of eastern Table 1; Wallace, 1972; Ehlers, 1997; Dehler unconformably overlain by Paleozoic strata Uinta Mountain Group strata represent part of a et al., 2007; Brehm, 2008; Kingsbury, 2008). (Figs. 1 and 2A; Hansen, 1965). The basal Jessie large west- and southwest-fl owing braided river In the eastern Uinta Mountains, near the Ewing Canyon Formation represents multiple system that was subjected to at least two marine Colorado-Utah border, a thicker section of south-fl owing alluvial fans and associated fan transgressions represented by laterally extensive the Uinta Mountain Group (~7 km) is exposed deltas that interacted with regional west- and (10s–100s of km) intervals of shale and fi ne- and comprises cross-bedded orthoquartzite and north-fl owing braided fl uvial, deltaic, and shal- grained sandstone of the Outlaw Trail formation sandstone with lesser siltstone, shale, and low marine environments (Table 1; e.g., Sander- and the Red Pine Shale (Fig. 2A, Dehler et al., conglomerate; it lies unconformably on the son and Wiley, 1986; Brehm, 2007; Dehler 2007; Rybczynski, 2009).

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The western and eastern units of the C Uinta Mountain Group are correlated using lithostratigraphy and low-resolution sequence RP03B(12) fault stratigraphy (Fig. 2A). The Red Pine Shale, the Red Pine Red Pine Shale 69PL05(11) RPS uppermost formation in the Uinta Mountain datum Group (≤1800 m thick), is the only mappable 140PL02(10) unit exposed throughout the Uinta Mountains; the base of this shale unit can be mapped along C strike for 165 km on the north side of the

range (Bryant, 1997; Rybczynski, 2009). Fur- MF Hades Pass Hades Pass ther correlation in the Uinta Mountain Group S3

Hades Pass qtzite. Hades Pass 31PLP06(9) is based on three upward-fi ning cycles (km MFF S3? S3 thick; S1–S3, Fig. 2A), which represent fl uvial 74PL05(8) to marine deposition. It is possible that some MA of the sequence boundaries, in particular the Fm. 36PL06(7)

122PL02(2) Mt.Watson basal one (S1), can be traced westward into DH 73PL05(6) the Big Cottonwood Formation (Crittenden, Red MH 76PL05(5) 1976; Christie-Blick, 1997; Fig. 2). Castle ? Crouse Cyn fm. Cyn Crouse The Uinta Mountain Group represents depo- I.Lake S2? sition in an intracratonic extensional basin with S2? base not exposed S2 a roughly east-west–trending northern basin OT SCUMG-9(4) edge and an open, low-relief southern margin (766 Ma) (Fig. 1B, Table 1; Dehler et al., 2007), and is Big Cottonwood Formation Big Cottonwood DB entirely developed on autochthonous Lauren- tian continental crust (Karlstrom and Houston, 1984). The previously used term “rift basin” 91PL05(3) to describe the Uinta Mountain Group basin is LW 90PL05(1) JEC Fm problematic because there are no volcanic rocks RCQ S1 or signifi cant rift-type facies associated with the BIG COTTONWOOD FM UINTA MOUNTAIN GROUP UINTA MOUNTAIN GROUP Uinta Mountain Group (cf. Link, 1987; Prave, WASATCH RANGE WESTERN UINTA MTNS EASTERN UINTA MTNS 1999). Compiled data from previous work shows that the Uinta Mountain Group basin Key: was, at least in part, extensional. Relatively Shale coarser grained deposits and a greater percent- Sandstone Conglomerate, sandstone, shale age of immature sandstones are found upsection Crystalline basement 1 km throughout the Uinta Mountain Group strata on S1 Base of sequence the northern side of the range, inferring an east- Detrital zircon sample (location number) west–trending, basin-bounding fault (Hansen, Detrital zircon sample (Mueller et al., 2007) 1965; Wallace, 1972; Brehm, 2008; Rybczyn- A ski, 2009). Approximately 7 km of northward- thickening Uinta Mountain Group strata are Figure 2 (on this and following page). (A) Stratigraphic columns of the Big Cottonwood For- exposed in the hanging-wall of what was likely mation (BCF) and Uinta Mountain Group (UMG) showing: intervals where detrital zircon a south-dipping growth fault (now reactivated as samples were obtained; the existing means of correlation between the eastern UMG, the the Uinta-Sparks Laramide reverse fault), sug- western UMG, and the BCF; and general stratigraphic trends of the units. S1, S2, and S3 gesting that the basin was a north-tilted half- indicate low-order fi ning upward sequences, which show fl uvial or proximal marine units at graben (e.g., Sears et al., 1982; Bruhn et al., the base, becoming proximal to distal marine at the top. All units are Neoproterozoic unless 1986; Stone, 1993; Dehler et al., 2007; Kings- otherwise noted. C—Cambrian; MF—Mutual Formation; MFF—Mineral Fork Forma- bury, 2008; Rybczynski, 2009). This interpreted tion; LW—Paleoproterozoic(?) Little Willow Complex; DH—Deadhorse Pass formation; northern basin-bounding fault is roughly par- MA—Mount Agassiz formation; MH—Moosehorn Lake formation; RCQ—Paleoprotero- allel with the 1.7 Ga south-dipping Cheyenne zoic(?) Red Creek Quartzite; JEC—Jesse Ewing Canyon Formation; DB—Diamond Breaks belt suture zone (between the Wyoming Craton formation; OT—Outlaw Trail formation; RPS—Red Pine Shale. (Modifi ed from Ehlers and to the north and Paleoproterozoic basement to Chan, 1999; Dehler et al., 2007.) the south) and represents syn–Uinta Mountain Group reactivation on parts of that zone (Bruhn et al., 1983; Stone, 1993). Grand Canyon, Arizona (e.g., Young, 1981; variability in the Red Pine Shale of the upper Previous age constraints on the Uinta Moun- Vidal and Ford, 1985; Link et al., 1993), the Uinta Mountain Group is very similar to that of tain Group are sparse, yet correlation with the top of which is now known to be 742 ± 6 Ma the upper part of the Chuar Group (Vidal and Chuar Group data sets constrains it to ~740 Ma (U-Pb age on reworked tuff at the top of upper- Ford, 1985; Porter and Knoll, 2000; Dehler to 770 Ma (Fig. 2B). The Uinta Mountain Group most member; Karlstrom et al., 2000). The et al., 2005; Nagy and Porter, 2005). The fi rst has long been correlated with the Chuar Group of distinct microfossil assemblage and C-isotope appearance of vase-shaped microfossils and the

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CHUAR GROUP UINTA MOUNTAIN GROUP δ13C (‰ PDB) δ13C (‰ PDB) –35 –30 –25 –20 –15 –10 –35 –30 –25 –20 –15 –10 STURT? STURT* 742 Ma

Key: Diamictite Dolomite

Kwagunt Fm. Kwagunt Organic-rich shale Sandstone Breccia/conglomerate

Red Pine Shale Basalt

Basement 200 m Vase-shaped microfossil Bavlinella faveolata

Galeros Fm. Acritarch undifferentiated <766 Ma C Cerebrosphaera buickii <777 Ma Unconformity C <942 Ma OLDER PROT 1.1 Ga formations lower Older >1.7 Ga B

Figure 2 (continued). (B) Regional correlation of the Uinta Mountain Group, Utah, with the Chuar Group, Arizona, illustrating their shared features and similar ages of ~740–770 Ma. In the Chuar Group, the presence of Cerebrosphaera buickii (Nagy et al., 2009) suggests strata younger than ~777 Ma (Hill et al., 2000) and the ash at the top is ~742 Ma (Karlstrom et al., 2000). In the Uinta Mountain Group, the maxi- mum depositional age of ~766 Ma in the Outlaw Trail formation indicates the majority of the group, if not all, is younger than this age (this paper). The Red Pine Shale and the upper Chuar Group host similar fossil assemblages, including vase-shaped microfossils, considered to indicate a pre-Sturtian age (before the fi rst glacial episode of the Cryogenian; Vidal and Ford, 1985; Dehler et al., 2007). Corresponding organic carbon-isotope anomalies in the upper strata of both units show relatively positive isotope values declining to background values (Dehler et al., 2005; Dehler et al., 2007; Brehm, 2008). Total 7 km of Uinta Mountain Group not shown (see Fig. 2A). Sturtian deposits above Red Pine Shale extrapolated from relationships between Big Cottonwood Formation and Mineral Fork Formation to the west (Link et al., 1993). Older ages in sub-Chuar strata are from Timmons et al. (2005). Age of basement below Uinta Mountain Group is from Hansen (1965). Pink band shows proposed correlation between the Uinta Mountain Group and the Chuar Group. PDB—Pee Dee belemnite; Prot— Proterozoic; Sturt—Sturtian. abundance of the colonial bacteria Bavlinella 900 and 942 Ma, respectively, and come from with respect to its original location on the craton faveolata in both the Red Pine Shale and the U-Pb analysis of detrital zircons (Timmons (Crittenden, 1976; Ehlers et al., 1997). Ehlers upper Chuar Group suggest a pre-Sturtian age et al., 2005; Mueller et al., 2007). and Chan (1999) interpreted this formation to (>~726–660 Ma; Dehler et al., 2007; Hoff- represent fl uvial and marine deposition based man and Li, 2009; Nagy et al., 2009) (Fig. 2B). Big Cottonwood Formation on facies architecture and analysis, and the Paleo magnetic data from the Uinta Mountain presence of tidal rhythmites in some intervals. Group also suggest a mid-Neoproterozoic age The Big Cottonwood Formation, exposed in The Big Cottonwood Formation is interpreted (and correlation with the Chuar Group) based the central Wasatch Range east of Salt Lake City to have been deposited together with the Uinta on comparison with the apparent polar wander and areas to the west (Slate Canyon, East Tintic Mountain Group to the east in a tide-dominated path (APWP) for Laurentia (~800–740 Ma from Mountains, Stansbury Island, and Carrington estuary whereby a west-fl owing fl uvial system Chuar Group data; Weil et al., 2006). The micro- Island), is a 5-km-thick succession of sand- was intermittently drowned by the open ocean fossil Cerebro sphaera buickii was recently found stone, orthoquartzite, and argillite with a basal (Ehlers et al., 1997). Paleocurrent data show in the lower Chuar Group (Nagy et al., 2009). conglomerate interval (Figs. 1 and 2A). This three modes of fl ow directions (NW, SW, and This acritarch is thought to be an index fossil for unit is positioned structurally below the thrust SE), similar to paleofl ow trends in the Uinta pre-glacial strata younger than ~777 Ma (Hill sheets of the Sevier orogenic belt and, although Mountain Group units (Table 1). et al., 2000). Maximum depositional ages for the associated with thrust faults (several km of dis- The Big Cottonwood Formation basin has Uinta Mountain Group and the Chuar Group are placement), has not been signifi cantly displaced been interpreted as an intracratonic rift basin

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TABLE 1. PALEOFLOW, PALEOENVIRONMENTAL, AND PROVENANCE INFORMATION Detrital zircon noitamroF *atadtnerrucoelaP †§ Paleoenvironment# Petrography provenance References Red Pine Shale, Brehm (2008); Southerly** Prodelta Quartzose shale Mixed middle Rybczynski (2009)

Red Pine Shale, Southerly** Delta front Feldspathic arenite Archean Brehm (2008) lower

Wallace (1972); Hades Pass, n = 18* Subfeldspathic Fluvial deltaic Mixed Lee (2000); lower and upper arenite Kingsbury (2008)

n = 143†

Wallace (1972); Mount Watson, basal Marine, fl uvial? Quartz arenite Mixed Sanderson (1984); Kingsbury (2008) n = 20*

Wallace (1972); Dead Horse Pass Barrier bar system Subarkosic siltstone Mixed Kingsbury (2008) n = 170*

Wallace (1972); Moosehorn Lake Marine Quartz arenite Mixed + Neoprot. Rybczynski (2009) n = 3*

Wallace (1972); Red Castle Fluvial, tidal Arkose Archean Kingsbury (2008) n = 291*

Subfeldspathic Dehler et al. (2007); Outlaw Trail Estuary, fl uvial Mixed + Neoprot. arenite and shale Rybczynski (2009) n = 120*

Subfeldspathic Marine, fan delta Mixed + Neoprot. Brehm (2007) arenite

Jesse Ewing n = 37* Canyon Sanderson and Alluvial fan NA NA Wiley (1986)

n = 182† Quartz arenite Archean (basal), (basal), Chan et al. (1994); Big Cottonwood Fluvial tidal subfeldspathic mixed Ehlers and Chan (1999) siltstone (middle) n = 114† (middle) *Paleofl ow data from studies associated with this paper. †Paleofl ow data from other studies with palefl ow data expressed as rose diagrams. §Flow direction (black arrow) shows specifi c fl ow direction of interval sampled (where available). #Paleoenvironments shown as underlined are linked to detrital zircon samples. **Inferred from architecture, provenance

that was bounded on its northern edge by a by Mineral Fork time (i.e., Sturtian), and that the basin. Big Cottonwood Formation and Uinta westward continuation of the basin-bounding basal BCF conglomerate could refl ect rift onset Mountain Group sediments were likely depos- fault of the northern Uinta Mountain Group and be correlative with the basal conglomer- ited in different parts of the same intracratonic basin. Evidence for this includes: the northern ate of the Uinta Mountain Group (Crittenden, extensional basin (Link et al., 1993). pinchout of the Big Cottonwood Formation 1976; Christie-Blick, 1997; Ehlers et al., 1997). The timing of deposition of the Big Cotton- across a Laramide-age syncline, clasts of crys- The Big Cottonwood Formation, much like the wood Formation is unknown, but the unit is cor- talline basement in the overlying Mineral Fork Uinta Mountain Group, does not contain vol- related with the Uinta Mountain Group based Formation suggesting that there was no BCF canic rocks or a signifi cant amount of immature on lithostratigraphic and paleomagnetic data present to the north of the modern BCF outcrop facies that would be expected in a classic rift (e.g., Link et al., 1993; Ehlers and Chan, 1999;

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Dehler et al., 2001a). Further evidence for a Big Cottonwood Formation–Uinta Mountain A Location 2: 6 122PL02, middle Big Cottonwood Formation Group correlation includes similarity of paleo- Big Cottonwood Canyon current data, depofacies, and detrital zircon age subfeldspathic siltstone; tidal populations (Figs. 2A and 3; Table 1; Ehlers, 4 (56 analyses; 62 grains) 1997; Ehlers and Chan, 1999; this paper). The Big Cottonwood Formation is unconformably bracketed by the underlying Paleoprotero- 2 zoic(?) Little Willow Complex and the overly- Relative probability ing Neoproterozoic (Sturtian glacial) Mineral Fork Formation (Fig. 2A; Crittenden, 1976; Christie-Blick and Link, 1988). 10 Location 1: Number METHODS 90PL05, lower Big Cottonwood Formation mouth of Big Cottonwood Canyon 8 Stratigraphic Units Sampled for quartz arenite; fluvial-tidal (25 analyses; 52 grains) Detrital Zircons 6

Twelve samples were collected from the 4 Uinta Mountain Group (n = 10) and Big Cot- tonwood Formation (n = 2) (De Grey, 2005; 2 Brehm, 2007; Brehm, 2008; Kingsbury, 2008). The samples were collected to ascertain the detrital zircon provenance from a spectrum 700 11001500 1900 2300 2700 3100 of sandstone compositions throughout the Age (Ma) stratigraphic successions and from sandstone Figure 3 (on this and following page). (A) Relative probability plots, units representing different depositional envi- with stacked histograms for the two samples from the Big Cotton- ronments and/or different parts of the basin wood Formation. (Figs. 1 and 2A; Table 1; GSA Data Repository Table DR11). This sampling strategy comple- ments the detrital zircon study by Mueller et al. (2007), whose data were presented from four and/or shale. A heavy mineral concentrate was to be remarkably homogeneous, in which case samples of a limited geographic, paleoenvi- prepared from the total rock using standard the total number of grains run was less than in ronmental, and stratigraphic range (Figs. 1A crushing, washing, heavy liquid (specifi c grav- other samples. The analyses consisted of four to and 2). Eight of our samples are from the west- ity 2.96 and 3.3), and paramagnetic procedures six scans through the mass range, with a refer- ern Uinta Mountain Group, and two are from (Williams, 1998). Representative fractions of ence zircon analyzed for every fi ve unknown the eastern UMG. Collectively they span from the total zircon-rich heavy mineral concentrate zircon analyses (Williams, 1998, and references the base to the top of the entire group and were were poured onto double-sided tape, mounted therein). The data have been reduced using the collected along and across strike of the east- in epoxy together with chips of the reference SQUID Excel Macro of Ludwig (2003). west–trending northern margin of the Uinta zircons (Duluth Gabbro-FC1 and Sri Lankan- Pb/U ratios have been normalized relative to Mountain Group basin (Figs. 1A and 2A). The SL13, see below), sectioned approximately in a value of 0.01859 for the FC1 reference zircon, samples from the Big Cottonwood Formation half, and polished. Refl ected and transmitted equivalent to an age of 1099 Ma (see Paces and are from the basal (fl uvial-tidal) interval and light photomicrographs were prepared for all Miller, 1993). Uncertainties given for individual from the middle interval where tidal rhythmites zircons. Cathodoluminescence (CL) scanning analyses (ratios and ages) are at the one sigma are present (Fig. 2A and Table 1). electron microscope (SEM) images were pre- level; however, the uncertainties in concor- pared for all zircon grains and used to examine dia age are reported as 95% confi dence limits. Geochronology the internal structures of the sectioned grains. Wetherill concordia plots (Fig. DR1 [see foot- The U-Th-Pb analyses were made using a note 1]), probability density plots with stacked U-Pb zircon analyses were performed on the combination of SHRIMP I, SHRIMP II, and histograms, and concordia age calculations 12 samples described above (Tables 1, DR1, and SHRIMP reverse geometry (RG) at the Re- were carried out using ISOPLOT/EX (Ludwig, DR2 [see footnote 1]). Our samples were sepa- search School of Earth Sciences, the Austra- 2003). For grains that are less than 1000 Ma, the rated from several kg of sandstone, siltstone, lian National University, Canberra, Australia. 206Pb/238U age was used for the relative prob- For the provenance studies, the zircons were ability plots, and for those over 1000 Ma, the 207 206 1GSA Data Repository item 2010129, Table DR1: analyzed sequentially and randomly with total Pb/ Pb age was employed. Analyses that are Sample locations; Tables DR2.1 through 2.12: Data number of grains analyzed ranging from 30 to more than 20% discordant were not included in for all 12 detrital zircon sample SHRIMP analyses; 72 grains, except for one special case where the relative probability plots. However, samples Table DR3: Petrographic data for 12 detrital zircon 128 grains were analyzed (see discussion of 76PL05 and 90PL05 are dominated by Archean samples; Figure DR1: Wetherhill plots for all 12 de- trital zircon sample SHRIMP analyses, is available sample SCUMG-9 below). In some cases, as age grains, many of which are metamict, have at http://www.geosociety.org/pubs/ft2010.htm or by determined from CL imaging and resultant lost radiogenic Pb, and so are greater than 20% request to [email protected]. U-Pb ages, the zircon populations were deemed discordant. From Wetherill concordia plots, it

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B Location 7: 36PL06, Deadhorse Pass fm. Location 12: RP03-B, middle Red Pine Shale Gilbert Peak, High Uintas Hades Creek. south flank, Uintas subarkosic siltstone; marine quartz siltstone; distal deltaic (28 analyses; 42 grains) (25 analyses, 30 grains)

Location 6: 73PL05, Moosehorn Lake fm. Location 11: 69PL05, lower Red Pine Shale Provo River headwaters type section, Red Pine Creek fine-grained quartz arenite; marine feldspathic arenite; proximal deltaic (52 analyses; 61 grains) (35 analyses, 40 grains)

Location 5: 76PL05, Red Castle fm. Location 10: 140PL02, upper Hades Pass fm.

Christmas Meadows, Stillwater River; fluvial Henrys Fork, High Uintas Relative probability coarse-grained arkosic arenite; fluvial subfeldspathic arenite; fluvial-deltaic (18 analyses; 30 grains) (46 analyses, 60 grains)

Location 4: SCUMG-9, Outlaw Trail fm. 6 Location 9: 31PL06, lower Hades Pass fm. Browns Park, eastern Uintas Gilbert Peak, High Uintas subfeldspathic arenite and shale; estuary 5 subfeldspathic arenite; fluvial-deltaic (106 analyses, 128 grains) (67 analyses; 72 grains) 4

3

2

1

Location 3: 91PL05, Jesse Ewing Canyon Fm. Location 8: 74PL05, Mount Watson Fm. type section, Jesse Ewing Canyon Bald Mountain, High Uintas coarse-grained subfeldspathic arenite; quartz arenite; marine marine (53 analyses; 57 grains) (40 analyses, 72 grains)

Figure 3 (continued). (B) Relative probability plots, with stacked histograms for the ten samples from the Uinta Mountain Group. See Figure 2A for corresponding stratigraphic data and Tables DR2 and DR3 [see footnote 1] for additional detrital zircon analytical data.

1692 Geological Society of America Bulletin, September/October 2010 Downloaded from gsabulletin.gsapubs.org on May 29, 2010 Maximum depositional age and provenance of the Uinta Mountain Group and Big Cottonwood Formation, northern Utah is clear that this discordance arises from radio- sistent with rapid crystallization in a vol canic genic Pb loss at or near the present day, because to subvolcanic setting. The style of internal the data defi ne a simple lead loss discordia line. CL zoning is consistent with a felsic igneous In these specifi c cases, the 207Pb/206Pb age is paragenesis; the zircons are not from a mafi c considered to refl ect the crystallization age of igneous source where broader or subdued CL the detrital zircons (Fig. DR1 [see footnote 1]), structure would be present (Corfu et al., 2003). and thus were included in our spectra. If one were to exclude all such discordant analyses, RESULTS the data set would be biased against these sig- 200 μm Grain 1 nifi cantly older grains. It should be noted that Maximum Depositional Age of the Uinta the analyses for sample 36PL06 also show sig- Mountain Group nifi cant discordance. However, in this case, the Wetherill concordia plot (Fig. DR1 [footnote 1]) After analyzing a total of ~128 zircon shows that the radiogenic Pb loss did not oc- grains (Table DR2 [see footnote 1]) in sample cur at or near the present day. In this case, the SCUMG-9, we identifi ed the four youngest 207Pb/206Pb ages for such discordant analyses are analyses that are within analytical uncertainty not considered to refl ect the crystallization age of each other, and these give a concordia age at of the zircon, and so they were excluded from 766.4 ± 4.8 Ma (Figs. 4 and 5). Similar single- Grain 12 the relative probability plots. grain U-Pb dates are recorded in the Jesse 200 μm Ewing Canyon Formation sample (91PL05) SCUMG-9 Sample from Outlaw and the Moosehorn Lake formation sample Trail formation (73PL05) (Fig. 3B). Unfortunately, these are isolated single-grain analyses and so individu- As with the other samples, zircon grains ally are not yet considered to be depositional (n = 50) from sample SCUMG-9 (Swallow age constraints. Nevertheless, the presence of Canyon-UMG-9) were fi rst analyzed in a ran- grains less than 800 Ma in three samples from the lower-middle Uinta Mountain Group in dom manner in order to determine the detrital Grain 38 zircon age distribution (Fig. 3). Within these 50 both the eastern and western parts of the range, randomly selected grains, one had a concordant in different stratigraphic levels, including the age of ~770 Ma, and we analyzed a second area very basal formation, adds further support to a on this sectioned grain to confi rm the notable general age assignment for the Uinta Mountain young age. For the other 49 grains analyzed Group at <770 Ma. in this session, fi ve failed to yield meaningful The fact that there are only four out of 128 data, and the remaining 44 grains had U-Pb grains analyzed (3.1%) in SCUMG-9 that pro- 200 μm ages ≥880 Ma, with most ≥1000 Ma. It must vide the ~766 Ma date in the Uinta Mountain be noted, and in fact stressed very strongly, that Group demonstrates the diffi culty of recogniz- a single grain cannot truly defi ne the maximum ing small but important detrital zircon popula- age of deposition. There are many variables, tions in detrital zircon studies. This is in general not the least of which includes the potential for agreement with Vermeesch (2004), who cal- the youngest grain being a contaminant of the culated that in the worst case scenario, at least laboratory processing. We hand selected ad- 117 grains are required in order to have 95% ditional grains from that fi rst mineral separa- confi dence that one has identifi ed a group of tion and collected a second sample suite from ages that comprises 5% of the total population Grain 41 the same stratigraphic interval; we then car- (cf. Stewart et al., 2001; Mueller et al., 2007). ried out another complete mineral separation. From the initial analyses of sample 31PL06, Zircon grains from both samplings were hand grain 8 gave a slightly discordant age of just selected on the basis of similar physical charac- less than 700 Ma (207Pb/206Pb date of 697 ± teristics—least rounded, subhedral to euhedral 9 Ma, ~5% discordant). This is anomalously grains, with zoned igneous internal structure on young, because the other 56 grains analyzed 200 μm the basis of the CL imaging (Fig. 4). From a are Grenvillian or older (Fig. 3; Table DR2 [see Figure 4. Combined transmitted light photo- population of many hundreds of grains (com- footnote 1]). A replicate analysis of this grain micrographs and cathodoluminescence (CL) bined from two fi eld samplings), and an addi- confi rms the original date. In the course of this scanning electron microscope images of the tional 78 SHRIMP U-Pb analyses, three more replication, a further 15 grains were targeted young grains (766 Ma) analyzed from the young grains with the same ~770 Ma age were in an attempt to fi nd another similarly young SCUMG sample, Outlaw Trail formation. identifi ed (Fig. 4; Table DR2 [see footnote 1]). grain, but only Grenvillian or older were re- Grains labeled as per Table DR2.4 [see foot- The four grains have widely different morphol- corded. Grain 8 is not a simple euhedral grain note 1]. The areas analyzed are shown on ogies, ranging from subrounded, more equant that might be expected for a volcaniclastic zir- the CL image. grains (grains 1 and 38) to elongate, to sub- con dating the youngest deposition. The grain hedral grains (grains 12 and 41) (Fig. 4). It is is dark colored and high in U (~1780 and 2645 notable that grain 12 has internal cavities con- ppm, respectively, for the two analyses) and

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Data-point error ellipses are 68.3% confidence radiogenic Pb loss, but still defi ne a prominent 0.136 207Pb/206Pb age peak at ~2685 Ma. Concordant grains in the lower Red Castle Formation de- 0.132 800 fi ne a single peak at 2600 Ma, whereas zircons from the lower Red Pine Shale have a more dis- persed age spectrum with prominent peaks at ~2645 Ma and 2710 Ma (Fig. 3). All three sam-

U 0.128 ples have few to no grains older than 2800 Ma. 238 760 We infer that the source for the Uinta Moun-

Pb/ 0.124 tain Group feldspathic deposits was on the

206 southern margin of the Wyoming province (SAT—Southern Accreted Terranes of Mueller 0.120 Concordia age = 766 ± 5 Ma and Frost, 2006). Petrographic, facies, paleocur- 720 (1σ, decay-constant errors included) rent, and detrital zircon data together indicate MSWD (of concordance) = 0.66, that fi rst-cycle sediment was derived from igne- Probability (of concordance) = 0.42 0.116 ous and/or metaigneous sources exposed along 0.98 1.02 1.06 1.10 1.14 1.18 1.22 1.26 the southern part of the Wyoming Craton and deposited in deltaic systems on the northern side 207Pb/235U of the Uinta Mountain Group basin (Table 1; Table DR3 [see footnote 1]). The strong Archean Figure 5. Concordia plot from SCUMG-9 (Outlaw Trail formation) peak in the Red Pine Shale, the youngest unit showing concordia age of 766 ± 4.8 Ma (supplemental data in Table of the Uinta Mountain Group, and in the lower DR2.4 [see footnote 1]). MSWD—mean square of weighted deviates. Red Castle formation, one of the oldest units in the western Uinta Mountain Group, and the presence of similar Archean peaks in all other has likely lost radiogenic Pb. This single grain Two of these are feldspathic samples from the samples, indicates that local northern source is the only one of this age that was found out Uinta Mountain Group (76PL05 and 69PL05), area(s) continuously contributed immature sedi- of the overall total of 704 grains analyzed and, and one is a quartz arenite from the basal Big ment throughout deposition of the Uinta Moun- while interesting, no geological signifi cance Cottonwood Formation (90PL05) (Figs. 3 tain Group (Figs. 2A and 3; Table 1). is placed on this single grain. Indeed, many and 6; Tables DR2 and DR3 [see footnote 1]). Unlike the Uinta Mountain Group feld- geological data sets indicate that the Uinta Those from the BCF have suffered signifi cant spathic samples mentioned above, the basal Big Mountain Group is ~740–770 Ma, including correlations with the Big Cottonwood Forma- tion (which is overlain by presumed Sturtian Qt 100 Mineral Fork Formation) and the Chuar Group (~740–~770 Ma) (Figs. 2A and 2B). 90

Detrital Zircon Age Populations 80

Overall, from a total of 704 grains analyzed, 70 565 are considered signifi cant in terms of con- 60 cordance and/or have meaningful 207Pb/206Pb ages, and these have been used to construct 50 relative probability plots (Fig. 3; Table DR2 [see footnote 1]). Peaks are identifi ed at ~2700, 40 1650–1850 Ma, 1500–1600 Ma, 1400–1450 Ma, and 930–1200 Ma, in addition to the small popu- 30 lation of ~766 Ma grains. Archean and Gren- 20 villian grains occur in about equal proportions, with ~32% of the total grains analyzed in the 10 age range 2500–2755 Ma, whereas ~36.5% are between 930 and 1300 Ma. 0 FL0 10 20 30 40 50 60 70 80 90 100 Archean Detrital Zircon Age Populations Mixed Archean only (2.5–2.8 Ga) Mixed + Neoproterozoic All 12 samples contain some Archean grains with a dominance of grains at 2600–2700 Ma (see Figure 6. Ternary diagram showing relationship between sandstone Fig. 3). Three samples (lower Big Cottonwood, composition and detrital zircon age populations. Note that there is lower Red Pine Shale, and lower Red Castle not a direct correlation between composition and detrital zircon formations) contain solely Archean grains. provenance. See Table DR3 [footnote 1] for petrographic data.

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Cotton wood Formation sample with the uni- the Mojave, Yavapai, and Mazatzal–Central Middle-Late Mesoproterozoic (9.3–1.2 Ga) modal Archean-age population is a texturally Plains provinces. Most of these grains, like other Detrital Zircon Age Populations mature, fi ne-grained quartz arenite of fl uvial- Proterozoic grains in this study, were transported Nine samples contain grains ultimately de- tidal origin (Ehlers and Chan, 1999) (Fig. 6, from the east, northeast, and southeast via fl u- rived from the 930–1200 Ma Grenville-age ter- Table DR3 [see footnote 1]). The depofacies, vial, tidal, and/or long shore currents (Table 1; rane. The large proportion of Grenvillian grains petrography, and detrital zircon provenance Fig. 1B). The presence of the mixture of Archean reaffi rms the “Grenville fl ood” as reported by of this sample suggest that quartz-rich sands and Paleoproterozoic detrital zircon grains typi- Mueller et al. (2007), and extensively noted pre- were produced from fl uvial and tidal rework- cally coincides with a change in depofacies and viously in similar age rocks elsewhere in Lau- ing of feldspathic sands similar to those repre- demonstrates a trend seen on many stratigraphic rentia, Baltica, and Siberia (Rainbird et al., 1992, sented in the Uinta Mountain Group samples scales. For example, the basal Red Pine Shale 1997; Maclean et al. 2006; Cawood et al., 2007). with unimodal Archean grain-age populations. (sample 69PL05) is a delta-front deposit with a The Grenvillian grains are associated with the This does not appear to be the case in the Uinta unimodal Archean zircon age population (Figs. Paleoproterozoic and other Mesoproterozoic Mountain Group, however, where quartz are- 2A and 3; Table 1). Above this interval, the Red grain-age populations and a wide range of paleo- nite samples show a mixture of Archean and Pine Shale (sample RP03B) shows transgression fl ow directions indicating a mixing of popula- Proterozoic grain-age populations (Table 1). to a distal prodelta setting with mixed Archean tions from multiple source areas. On the other The westerly and northerly paleofl ow directions and dominantly Paleoproterozoic detrital zircon hand, some samples show a correlation between in the Big Cottonwood Formation are supportive grains (Dehler et al., 2007; Brehm, 2008). The large populations of Grenvillian grains and over- of reworking by longitudinal rivers or tides (by Paleoproterozoic provenance signature is con- all westerly paleofl ow (Table 1), suggesting deri- comparison to facies and paleofl ow in the Uinta sistent with Nd-isotope values from many of vation from the Grenville orogen and its foreland Mountain Group, Table 1). Alternatively, these the Uinta Mountain Group and Big Cottonwood to the east (e.g., Link et al., 1993; Mueller et al., grains could have been derived from a quartz- Formation shale samples analyzed by Condie 2007; Baranoski et al., 2009). The river system rich source on the Wyoming craton, now eroded et al. (2001). Petrographic results from these that fl owed through and/or into the Uinta Moun- or covered, that supplied sediment to the incipi- nine samples again show that sandstone compo- tain Group–Big Cottonwood Formation basin ent basin in the Big Cottonwood area (Fig. 6; sition does not consistently correlate with a spe- supplied major numbers of Grenvillian zircons Table DR3 [see footnote 1]). The wide range cifi c source area (Fig. 6). to the western margin of Laurentia and the proto- in sandstone composition of these three Uinta Pacifi c (Fig. 7). Mountain Group–Big Cottonwood Formation Early Mesoproterozoic (1.5–1.6 Ga) Detrital The Big Cottonwood Formation tidal rhyth- samples with unimodal Archean grain popula- Zircon Age Population mite sample (122PL02) is dominated by a Gren- tions shows that composition is not necessarily a There is a minor but significant 1500– villian detrital zircon population (Fig. 3A). This refl ection of provenance, as has been the general 1600 Ma age peak in four of the samples from is in stark contrast to the other sample from model for UMG provenance (Fig. 6). the Uinta Mountain Group and Big Cotton- the basal BCF, which has only Archean zircon Whole rock Nd-isotope data from Big Cot- wood Formation (Fig. 3). The ultimate source grains. This is another good example (like the tonwood Formation, Red Pine Shale, and Red for these grains may be from Australia (e.g., Red Pine Shale samples) of what is likely caus- Castle shale samples (Condie et al., 2001; sam- Gawler Range Volcanics), but a more proxi- ing the provenance change in the Big Cotton- ple locations not reported) suggest a dominantly mal and likely source could be reworked lower wood Formation–Uinta Mountain Group strata: Paleoproterozoic or mixed Paleoproterozoic– Belt Supergroup equivalents (e.g., Ross and the marine or relatively distal depofacies have Archean source rather than the Archean prove- Villeneuve, 2003; Link et al., 2007) and/or the mixed populations, and the fl uvial-infl uenced or nance shown in our detrital zircon data. Because Pinware terrane in northeastern Canada (Rain- more proximal (northern) depofacies are domi- unimodal Archean detrital zircon populations bird et al., 1997; Heaman et al., 2004). This nated by Archean grains. were found in coarse- and fi ne-grained sand- grain-age population has thus far only been stone samples, grain size alone does not explain found in the middle part of the two successions Neoproterozoic (~766 Ma) Detrital Zircon the differences in zircon provenance, at least in (Uinta Mountain Group and Big Cottonwood Age Population the sand fraction (Fig. 6; Table DR3 [see foot- Formation) and is associated with very promi- Three samples contain detrital zircons derived note 1]). As our understanding of the complex nent Grenvillian peaks; further analyses could from a 760–770 Ma source. The morphology sourcing of the Uinta Mountain Group and Big reveal that this is a signifi cant detrital zircon and internal CL structure of the grains indicate a Cottonwood Formation basin unfolds, it may be stratigraphic-marker interval, perhaps indicat- felsic volcanic source for these zircons (Fig. 4). that the shale deposits sampled by Condie et al. ing a regional paleogeographic change. This These younger grains are from samples that (2001) were derived from Paleoproterozoic or idea is consistent with the proposed correlation have mixed provenance, and come from sub- mixed sources. In any case, the whole rock Nd between the Uinta Mountain Group and Big arkosic and/or quartz-rich sandstone and shale analyses, because they are a composite average Cottonwood Formation in Figure 2A. from similar marine depofacies (Table 1; Figs. analysis of the total rock samples, record differ- 3B and 6). Sampled intervals of the Outlaw Trail ent chemical systematics than the more resilient Early-Middle Mesoproterozoic (1.4–1.45 Ga) (SCUMG-9), Jesse Ewing Canyon (91PL05), single zircon data presented herein. Detrital Zircon Age Populations and Moosehorn Lake (73PL05) formations Seven of the samples yielded an age popula- show north-northwesterly paleofl ow indicating Paleoproterozoic Detrital Zircon Age tion of 1.4 to 1.45 Ga. These zircons probably fi nal transport was by marine currents coming Populations (1.65–1.85 Ga) were ultimately sourced from A-type igneous from the south-southeast (Table 1). Paleoproterozoic detrital zircons are present rocks that were emplaced across Laurentia be- There are several possible sources for the in nine of the samples. They range in age from tween 1330 and 1480 Ma (Van Schmus et al., ~760–770 Ma grains. In eastern Laurentia, 1650 to 1850 Ma and were derived from source 1993) or reworked from the Belt basin to the rhyolite in the Mount Rogers Formation is areas in the juvenile Paleoproterozoic crust of north (Link et al., 2007). ~760 Ma (Aleinikoff et al., 1995), and some

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Figure 7. Paleotectonic recon- MM Am. Baltica modal volcanism and normal faulting recorded struction at ~750 Ma modi- Australia in the ~680–720 Ma formations along the Cor- fi ed from Goodge et al. (2008) dilleran margin (e.g., Pocatello, Kingston Peak, showing transcontinental Uinta Mineral Fork, Perry Canyon, and Edwards- Mountain Group river system burg formations) and subsequent formation of tapping Grenvillian sources, a west-facing passive margin after 650 Ma crossing the Mid-Continent rift (Christie-Blick, 1997; Lund et al., 2003; Fan- (gray areas), entering the Uinta Divide ning and Link, 2004, 2008). The Adelaide rift Mountain Group–Big Cotton- East complex (~777 Ma) and rift basins in south Antarctica wood Formation fl uvial-marine UMG/BCF China (745–780 Ma) and Namibia (758.5 ± system (outcrop extent shown CG ville highlands 3.5 Ma) are roughly coeval with the ~740– GrenvilleGren highlands in larger black area), and de- Ocean Laurentia ? 770 Ma Laurentian intracratonic basins, sup- livering Grenvillian grains to porting the idea of a time-transgressive breakup adjacent peri-Gondwanan conti- of Rodinia (Hoffman and Halverson, 1996; nental margins (black arrows). Hoffman et al., 1998; Preiss, 2000; Eyles and Also shown are the potentially coeval Shaler and related river systems in northern Lau- Januszczak, 2003; Li et al., 2003). rentia (Rainbird et al., 1992, 1997). See text for discussion. Abbreviations: UMG—Uinta Mountain Group; BCF—Big Cottonwood Formation; MM—Mackenzie Mountain basin; Provenance Am—Amundsen basin; CG—Chuar Group. Short dashed line shows hypothesized shore- line during maximum transgression onto western Laurentia at ~766 Ma. The detrital zircon age populations presented in this paper generally reaffi rm the interpreta- tions of Condie et al. (2001), among others, plutonic rocks of the Crossnore Complex in the middle Pahrump Group of Death Valley holds that sediment was sourced both from the north, North Carolina Blue Ridge are between 750 and (e.g., Link et al., 1993; Rainbird et al., 1996; from the Archean Wyoming province, and from 760 Ma (Su et al., 1994). There are no known Dehler et al., 2001b), it is possible that all of the east, from a major river parallel with the felsic sources of this age in western Laurentia. these units were deposited after ~770 Ma, in a strike of the Cheyenne Belt and the fabric of Considering the paucity of ~766 Ma grains in series of coeval, and possibly connected marine the Paleoproterozoic accreted crust of Colorado the Uinta Mountain Group, it is possible that basins in southwestern Laurentia (the ChUMP (Fig. 1B). This large west-fl owing fl uvial system the zircons were the product of an ashfall event Interior Seaway; Dehler, 2008). This age range contained detrital zircons from 1650 to 1850 Ma from eastern Laurentia or the proximal con- is consistent with constraints on Succession juvenile Paleoproterozoic crust of the Mojave, jugate Rodinia rift margin, such as from the B strata in Canada, which also record intra- Yavapai, and Central Plains provinces, 1450 Ma 777 ± 7 Ma Boucaut Volcanics of the Nackara cratonic basin development at this general time A-type granites of Colorado, and 930–1200 Ma Arc in South Australia (Preiss, 2000). Regard- (>723 Ma to <1070 Ma; Rainbird et al., 1996, Grenvillian terranes (Fig. 1B). In addition to less of the primary source, the 766 Ma grains and references therein). derivation from the Wyoming Province to the appear to be unique to marine depofacies and Correlations with strata farther afi eld suggest north, Archean detrital zircons were also likely were ultimately carried via marine currents dur- that the transgressions documented in the Uinta delivered from the Superior craton to the north- ing transgressions. Mountain Group–Big Cottonwood Formation east (Fig. 1B), which is consistent with a com- basin were eustatically driven. In addition to mon southwesterly paleofl ow associated with DISCUSSION the development of marine intracratonic basins the alluvial and fl uvial depofacies of the east- in Laurentia at ~740–770 Ma, major marine in- ern Uinta Mountain Group (Table 1; Sanderson Paleogeography and Tectonics undation also commenced at ~760–770 Ma in and Wiley, 1986; De Grey and Dehler, 2005; the Adelaide rift complex of Australia (Preiss, Rybczynski, 2009). The maximum depositional age of the Out- 2000) and is coincident with the development A minor, but signifi cant, number of previ- law Trail formation, which, along with the of other marine intracratonic basins of this gen- ously unrecognized mid-Neoproterozoic zir- Jesse Ewing Canyon and Moosehorn Lake for- eral age (e.g., Akademikerbreen Group, north- con grains (~760–770 Ma) were derived from mations, hosts the 760–770 Ma zircon grains, east Svalbard and Eleonore Bay Group, east an unknown source and fi nally transported in a refi nes previously proposed correlations within Greenland [Knoll et al., 1986; Halverson et al., north-northwesterly direction within the Uinta Succession B of western North America. De- 2007]). These correlations suggest a pre-Sturtian Mountain Group–Big Cottonwood Formation trital zircon age populations from the Big and/or early Cryogenian interval of high global system during marine transgressions. The prov- Cottonwood Formation are nearly identical to sea level that was likely caused by increased enance change associated with these marine the Uinta Mountain Group age populations, seafl oor spreading rates as Rodinia rifted apart units, defi ned by detrital zircon populations, further supporting their correlation and paleo- (e.g., Asmerom et al., 1991; Preiss, 2000; Li paleocurrent data, and depofacies, suggest that geographic relationships. The maximum age of et al., 2003; Li et al., 2008). during transgressive episodes, young grains the UMG and correlative BCF is similar to the The Uinta Mountain Group, Big Cottonwood were reworked, and/or different sources were hypothesized age of the lower Chuar Group of Formation, and Chuar Group together record tapped to the south-southeast and integrated Grand Canyon (~770 Ma) and strengthens this intracratonic extension and sedimentation in with sediment continuously derived from the correlation. These correlations place the Uinta southwestern Laurentia at ~740–770 Ma that north and east via deltaic and/or fl uvial systems Mountain Group, Big Cottonwood Formation, was likely related to the breakup of Rodinia (Fig. 1B; Table 1). During regressions there was and Chuar Group at the top of Succession B in (Dehler et al., 2001a; Timmons et al., 2001; this less mixing of grain populations, especially southwestern Laurentia. If correlation with the paper). This would have taken place prior to bi- proximal to the basin edges.

1696 Geological Society of America Bulletin, September/October 2010 Downloaded from gsabulletin.gsapubs.org on May 29, 2010 Maximum depositional age and provenance of the Uinta Mountain Group and Big Cottonwood Formation, northern Utah

The Fate of Grenvillian Sediment mations, central and southern Appalachians: Evidence De Grey, L.D., 2005, Geology of the Swallow Canyon Downstream of the Uinta Mountain for two pulses of Iapetan rifting: American Journal of 7.5-minute quadrangle, Daggett County, Utah and Science, v. 295, p. 428–454. Moffat County, Colorado: Facies analysis and stratig- Group–Big Cottonwood Formation Amato, J.M., Boullion, A.O., Serna, A.M., Sanders, A.E., raphy of the Neoproterozoic eastern Uinta Mountain River System Farmer, G.L., Gehrels, G.E., and Wooden, J.L., 2008, Group [M.S. thesis]: Idaho State University, 122 p. 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Uinta Mountain Geology: Utah Geological Association river system that transported Laurentian zircons, Asmerom, Y., Jacobsen, S.B., Knoll, A.H., Butterfi eld, N.J., Publication 33, p. 17–33. in particular the abundant 930–1300 Ma grains and Swett, K., 1991, Strontium isotopic variations Dehler, C.M., 2008, The Chuar Group–Uinta Mountain derived from the Grenville province, westward of Neoproterozoic seawater: Implications for crustal Group–Pahrump Group Connection Revisited: A evolution: Geochimica et Cosmochimica Acta, v. 55, snapshot of the infra-Sturtian Earth system: Geologi- to western Laurentia and ultimately to the incipi- p. 2883–2894, doi: 10.1016/0016-7037(91)90453-C. cal Society of America Abstracts with Programs, v. 40, ent marine basin formed by the early rifting of Ball, T.T., and Farmer, G.L., 1998, Infi lling history of a Neo- no. 1, p. 36. proterozoic intracratonic basin: Nd isotope provenance Dehler, C.M., Elrick, M.E., Karlstrom, K.E., Smith, G.A., Rodinia (Fig. 7) (cf. Mueller et al., 2007). This studies of the Uinta Mountain Group, western United Crossey, L.J., and Timmons, M.J., 2001a, Neo- river system may have been coeval with other States: Precambrian Research, v. 87, p. 1–18, doi: protero zoic Chuar Group (~800–742 Ma), Grand pan-continental river systems in northern Lau- 10.1016/S0301-9268(97)00051-X. Canyon: A record of cyclic marine deposition during Baranoski, M.T., Dean, S.L., Wicks, J.L., and Brown, V.M., global cooling and supercontinent rifting: Sedimen- rentia that were also tapping the Grenville oro- 2009, Unconformity-bounded seismic refl ection se- tary Geology, v. 141–142, p. 465–499, doi: 10.1016/ gen (Young et al., 1979; Rainbird et al., 1992, quences defi ne Grenville-age rift system and foreland S0037-0738(01)00087-2. 1997). Limited geochronologic control on the basins beneath the Phanerozoic of Ohio: Geosphere, Dehler, C.M., Prave, A.R., Crossey, L.I., Karlstrom, K.E., v. 5, no. 2, p. 140–151. Atudorei, V., and Porter, S.M., 2001b, Linking mid- Shaler and Mackenzie Mountain supergroups Brehm, A.M., 2007, A re-evaluation of the Jesse Ewing Neoproterozoic successions in the western U.S.: The (>723 Ma and <1070 Ma), which record these Canyon Formation, Uinta Mountain Group, northeast- Chuar Group–Uinta Mountain Group–Pahrump Group ern Utah [M.S. thesis]: Logan, Utah State University, connection (ChUMP): Geological Society of America northern fl uvial systems, makes this paleogeo- 232 p. Abstracts with Programs, v. 33, no. 5, p. 20–21. graphic interpretation uncertain. Brehm, C.A., 2008, Sedimentology, stratigraphy, and organic Dehler, C.M., Elrick, M.E., Bloch, J.D., Karlstrom, K.E., Though Rodinia reconstructions are under geochemistry of the Red Pine Shale, Uinta Mountains, Crossey, L.J., and Des Marais, D., 2005, High- Utah: A prograding deltaic system in a “Western Neo- resolution δ13C stratigraphy of the Chuar Group debate, the confi guration shown by Goodge proterozoic Seaway” [M.S. thesis]: Logan, Utah State (~770–742 Ma), Grand Canyon: Implications for mid- et al. (2008) places the Uinta Mountain Group– University, 324 p. Neoproterozoic climate change: Geological Society Big Cottonwood Formation basin such that it Bruhn, R.L., Picard, M.D., and Beck, S.L., 1983, Mesozoic of America Bulletin, v. 117, no. 1–2, p. 32–45, doi: and early Tertiary structure and sedimentology of the 10.1130/B25471.1. may have been an avenue for Grenvillian zir- central Wasatch Mountains, Uinta Mountains, and Dehler, C.M., Porter, S.M., De Grey, L.D., Sprinkel, D.A., cons to reach not only the western Laurentian Uinta basin: Utah Geological and Mineralogical Sur- and Brehm, A., 2007, The Neoproterozoic Uinta vey Special Studies, no. 59, p. 63–105. Mountain Group Revisited: A synthesis of recent work margin but also peri-Gondwanan Neoprotero- Bruhn, R.L., Picard, M.D., and Isby, J.S., 1986, Tectonics on the Red Pine Shale and related undivided clastic zoic continental margins. This may have pro- and sedimentology of the Uinta Arch, Western Uinta strata, Northeastern Utah, in Link, P.K., and Lewis, vided a way for large quantities of Grenvillian Mountains, and Uinta Basin, in Peterson, J.A., ed., R.S., eds., Proterozoic Geology of western North Paleo tectonics and sedimentation in the Rocky Moun- America and Siberia: Society for Sedimentary Geol- zircons to be reworked into latest Neoprotero- tain region, United States: American Association of ogy (SEPM) Special Publication 86, p. 151–166. zoic sands on several continental margins of Petroleum Geologists Memoir 41, p. 333–352. Ehlers, T.A., 1997, Tidal sedimentation and tectonics in the eastern Gondwana (Ireland et al., 1998) that Bryant, B., 1997, Geologic and structure maps of the Salt Proterozoic Big Cottonwood Formation, Utah [M.S. Lake City 1° × 2° quadrangle, Utah and Wyoming: thesis]: Salt Lake City, University of Utah, 108 p. otherwise have no known viable Grenvillian U.S. Geological Survey Miscellaneous Investigations Ehlers, T.A., and Chan, M., 1999, Tidal sedimentology and source. This idea requires that the proto–Pacifi c Series Map I-1997, 3 sheets, scale 1: 125,000. estuarine deposition of the Proterozoic Big Cotton- Cawood, P.A., Nemchin, A.A., Strachan, R., Prave, T., and wood Formation, Utah: Journal of Sedimentary Re- Ocean separating Laurentia from Antarctica Krabbendam, M., 2007, Sedimentary basin and de- search, v. 69, no. 6, p. 1169–1180. and Australia maintained subdued topography trital zircon record along East Laurentia and Baltica Ehlers, T.A., Chan, M.A., and Link, P.K., 1997, Proterozoic and, hence, rifting had not yet commenced in during assembly and breakup of Rodinia: Journal tidal, glacial and fl uvial sedimentation in Big Cotton- of the Geological Society, v. 164, p. 257–275, doi: wood Canyon, Utah: Brigham Young University Geol- this part of the ocean basin. 10.1144/0016-76492006-115. ogy Studies, v. 42, no. 1, p. 31–58. Christie-Blick, N., 1997, Neoproterozoic sedimentation and Evans, K.V., Aleinikoff, J.N., Obradovich, J.D., and Fanning, ACKNOWLEDGMENTS tectonics in west-central Utah: Brigham Young Univer- C.M., 2000, SHRIMP U-Pb geochronology of volcanic sity Geology Studies, v. 42, p. 1–30. rocks, Belt Supergroup, western Montana: Evidence Christie-Blick, N., and Link, P.K., 1988, Glacial-marine for rapid deposition of sedimentary strata: Canadian Support was provided by the U.S. Geological Sur- sedimentation, Mineral Fork Formation (Late Protero- Journal of Earth Sciences, v. 37, no. 9, p. 1287–1300, vey, National Cooperative Geologic Mapping Pro- zoic) Utah, in Holden, G.S., ed., Geological Society of doi: 10.1139/cjes-37-9-1287. gram (Dehler and Link); the Utah Geological Survey America Annual Meeting Field Trip Guidebook 1988: Eyles, N., and Januszczak, N., 2003, “Zipper-rift”: A tec- Mapping Division; and the National Science Founda- Colorado School of Mines–Professional Contributions, tonic model for Neoproterozoic glaciations during the tion grant EAR-0819759 (Link, Dehler, and Yonkee). no. 12, p. 259–274. breakup of Rodinia after 750 Ma: Earth-Science Re- We thank graduate students Laura De Grey Ellis, Condie, K.C., Lee, D., and Farmer, G.L., 2001, Tectonic views, v. 65, p. 1–73. 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