Central Uinta Mountains, Utah
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Precambrian Research 236 (2013) 65–84 Contents lists available at ScienceDirect Precambrian Research jou rnal homepage: www.elsevier.com/locate/precamres Sequence stratigraphy and formalization of the Middle Uinta Mountain Group (Neoproterozoic), central Uinta Mountains, Utah: A closer look at the western Laurentian Seaway at ca. 750 Ma a,∗ a,1 a b Esther M. Kingsbury-Stewart , Shannon L. Osterhout , Paul K. Link , Carol M. Dehler a Department of Geosciences, M.S. 8072, Idaho State University, Pocatello, ID 83209, United States b Department of Geology, 4505 Old Main Hill, Utah State University, Logan, UT 83422, United States a r t a b i s c l e i n f o t r a c t Article history: The mid-Neoproterozoic (ca. 750 Ma) Uinta Mountain Group (UMG), northeast Utah, USA, records trans- Received 3 November 2012 gressions of an epicontinental sea at least 150 million years before inception of the Laurentian western Received in revised form 18 June 2013 passive margin. This work refines middle UMG stratigraphy by formalizing three lithostratigraphic Accepted 20 June 2013 formations and interpreting a sequence stratigraphic framework in the central part of the Uinta Moun- Available online 19 July 2013 tains. Middle UMG marine and fluvial-deltaic facies associations comprise eight depositional sequences within a kilometer-thick upward-fining composite sequence. These depositional sequences form one Keywords: progradational–aggradational (“lowstand”) sequence set (PASS) and one aggradational–progradational Neoproterozoic (“highstand”) sequence set (APSS). Depositional sequences were deposited within a tide- and wave- Uinta Mountain Group Rodinia affected epicontinental seaway that received sediment from a south-flowing fluvial system proximally Laurentia sourced in the Neoarchean southern Wyoming Province to the north and from a separate system of major, Sequence stratigraphy west-flowing trans-Laurentian rivers distally sourced in the Grenville orogen, the mid-continent granite Detrital zircon province, and the Yavapai and Mazatzal provinces to the south and east. Middle UMG fluvial-marine paleogeography strengthens the genetic link with the coeval Big Cotton- wood and Little Willow formations (Utah), the Chuar Group (Arizona), and upper Pahrump Supergroup (California), which collectively indicate a ca. 770–740 Ma epicontinental seaway existed across much of western Laurentia before 700 Ma rifting and 600 Ma formation of the Cordilleran passive margin. Long- term marine transgression onto continental Laurentia was likely caused by supercontinent breakup, particularly rifting of the Tarim and South China blocks from the remainder of Rodinia. Poorly con- strained autocyclic drivers (delta lobe switching, channel avulsion) and allocyclic drivers (climatic fluctuations, local tectonism) controlled higher frequency depositional cycles superimposed on this long- term transgression. Western Laurentia thus records prolonged (750–600 Ma) episodic basin formation, mafic volcanism, and faulting before establishment of a continental terrace after 600 Ma. The Neopro- terozoic western Laurentian epicontinental seaway can be used as a tie-point with other continents to help constrain the original continental configuration of Rodinia. Published by Elsevier B.V. 2 1. Introduction Group (UMG), northeast Utah, USA (Fig. 1), making these rocks among the longest recognized stratigraphic units in North Amer- The pioneering Powell, King, and Hayden geological surveys of ica (Powell, 1876; Emmons, 1877). Despite its superb exposure, the mid 1800s first documented the Precambrian Uinta Mountain UMG stratigraphy (and therefore paleogeography) is only grossly resolved, due to remote location, great thickness, lithologic repe- tition and related lack of marker units or other regional timelines. Over 2 km of the middle part of the UMG are exposed in the area of ∗ Kings Peak, Mount Powell, and Red Castle on the crest of the Uinta Corresponding author at: Wisconsin Geologic and Natural History Survey, Madi- son, WI, United States. Tel.: +1 608 263 3201; fax: +1 608 262 8086. Mountain anticline (Figs. 1 and 2; Bryant, 1992). Lateral and ver- E-mail addresses: [email protected] (E.M. Kingsbury-Stewart), tical facies relationships and stratal geometries define a hierarchy [email protected] (S.L. Osterhout), [email protected] (P.K. Link), [email protected] (C.M. Dehler). 1 Currently with Pioneer Natural Resources, Denver, CO. Research completed 2 while at Idaho State University. Uinta Mountain Group (UMG). 0301-9268/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.precamres.2013.06.015 66 E.M. Kingsbury-Stewart et al. / Precambrian Research 236 (2013) 65–84 Fig. 1. (A) Regional geologic map of Uinta Mountains, showing Kings Peak and Mount Powell quadrangles, and localities mentioned in the text. Modified after Haddox et al. (2005). (B) Simplified geologic map of north-central Uinta Mountains in the area of the Kings Peak and Mount Powell quadrangles. Boxes locate stratigraphic sections shown in Fig. 5. Triangles locate major mountain peaks. Zuc = Red Castle For- Fig. 2. Photopanel of the east wall of the Henry’s Fork drainage above Dollar Lake mation; Zuda = Dead Horse Pass and Mount Agassiz formations; Zuh = formation of showing stratal geometry and stratigraphic units. The box shows the zoomed-in Hades Pass. Base from D. Sprinkel, Utah Geological Survey, unpublished, with Kings area. The arrow points towards south. DS = Depositional sequence. Zuc: Red Castle Peak and Mount Powell quadrangles simplified from our mapping (Kingsbury, 2008; Formation; Zud: Dead Horse Pass Fm.; Zuma: Mount Agassiz Fm. Osterhout, 2011). Farmer, 1998; Condie et al., 2001; Dehler et al., 2010). The active of marine and marine through fluvial-deltaic successions that are northern margin of the half-graben was bounded by reactivated exposed, often in three dimensions, above tree line along later- structures along or south of the southern edge of the Archean ally continuous (km-scale) cirque walls along the crest of the Uinta Wyoming Province (Sears et al., 1982; Bryant and Nichols, 1988; Mountains (Figs. 1 and 2). These exposures are only found in the Stone, 1993; Nelson et al., 2002, 2011). Neoproterozoic normal remote parts of the range and offer insight into the more detailed faulting accompanied UMG deposition (Brehm, 2008; Kingsbury, nature of the UMG strata, therefore enhancing paleoenvironmental 2008; Rybczynski, 2009). Paleomagnetic studies suggest a near- and paleogeographic understanding of the UMG. equatorial paleolatitude (Weil et al., 2004, 2006). Our goal is to integrate several independent observations from Latest Neoproterozoic to early Cambrian normal faulting tilted the middle UMG in the middle part of the Uinta Mountain range and uplifted the UMG prior to deposition of Paleozoic strata (Stone, including detrital zircon age spectra, lithofacies and facies associ- 1993; Bryant, 1992). Extensional structures within the UMG basin ations, vertical stacking patterns, and stratal architecture exposed were inverted during Paleozoic contractional events, for example in outcrop to resolve the lithostratigraphy and sequence stratig- the late Pennsylvanian – early Permian Ancestral Rocky Moun- raphy of the middle UMG. Specifically, we (1) formalize three tains orogeny (Stone, 1993). Structural inversion and growth of geologic units (the Red Castle, Dead Horse Pass and Mount Agassiz the modern Uinta Mountains culminated in the Late Cretaceous to formations) to facilitate stratigraphic understanding of the Neo- mid-Cenozoic Laramide orogeny (Bradley, 1995; DeCelles, 2004). proterozoic section in the Uinta Mountains; (2) characterize UMG The UMG unconformably overlies Paleoproterozoic metamor- stratigraphy in terms of a hierarchy of accommodation-succession phic rocks along the northeastern edge of the Uinta Mountains (sensu Neal and Abreu, 2009); and (3) integrate these new data into (Hansen, 1965; Sears et al., 1982), but the base is not exposed in the regional understanding of the Neoproterozoic paleogeography the west (e.g., Wallace, 1972). Cambrian or Mississippian strata of western Laurentia. unconformably overlie the UMG (Hansen, 1965). The quartzose and arkosic UMG has been interpreted as a 2. Geologic setting sand-dominated, fluvial (Sanderson, 1978, 1984; Condie et al., 2001); fluvial-marine (Wallace and Crittenden, 1969; Wallace, The upper Precambrian (Neoproterozoic, Cryogenian) Uinta 1972; Dehler et al., 2010), or fluvial-lacustrine (Link, 1993; Winston Mountain Group contains up to 7 km of mainly red-colored and Link, 1993) system within an elongate basin that opened to the sandstone and mudrock, and is only exposed in the Uinta Moun- west and south (e.g. Hansen, 1965; Wallace and Crittenden, 1969; tains of northern Utah (Hansen, 1965;Fig. 1). Previous workers Dehler et al., 2010). The UMG contains three, km-thick, upward- have suggested deposition in an intracratonic half-graben with fining composite sequences (depositional sequences of Dehler et al., an east-west-trending northern margin (Hansen, 1965; Ball and 2010; Fig. 3). The lower composite sequence is only exposed in the E.M. Kingsbury-Stewart et al. / Precambrian Research 236 (2013) 65–84 67 Fig. 3. Generalized stratigraphic columns from the eastern and western Uinta Mountains. Composite sequence boundaries divide the Uinta Mountain Group into three major composite sequences. Abbreviations: CS, composite sequence; CSB, composite sequence boundary; CTS, composite transgressive surface; Deadhs., Deadhorse