in the type Sevier orogenic belt, western United States Thrust timing, growth of structural culminations, and synorogenic sedimentation

Most of the regional shortening in the type area of the Sevier orogenic belt in central Utah was accommodated by displacement on the Canyon Range (Neocomian-Aptian), Pavant (Aptian-Albian), Paxton (Cenomanian-Campanian), and Gunnison (late Campanian–Paleocene) thrust systems. Inception of each thrust system generated synorogenic sediment associated with frontal thrust-tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland. The Sevier culmination, a large antiformal duplex cored by crystalline basement rocks, developed during Paxton and Gunnison thrusting west of and structurally beneath the Canyon Range and Pavant thrusts. Growth of the Sevier culmination was coeval with reactivation of the Canyon Range and Pavant thrust systems and produced a second culmination in Proterozoic–Lower Cambrian rocks in the Canyon Range. These structural highs provided much of the sediment to the adjacent foreland basin from late Cenomanian to late Paleocene time, and may have helped to maintain critical taper in the thrust belt. INTRODUCTION The Sevier fold-thrust belt in the North American Cordillera is one of the most important thrust belts in the world, both because of its large scale and because it has been the source of many general principles of thrust belt geology (e.g., Armstrong, 1968; Dahlstrom, 1970; Royse et al., 1975). Ironically, where Armstrong (1968) first recognized the large scale of Sevier thrust faulting in central Utah, no consensus exists regarding the kinematic history of thrusting (e.g., Lawton, 1985; Villien and Kligfield, 1986; Yingling andHeller, 1992). This paper presents a revised scheme of thrust timing for central Utah, based mainly on recent work in the Canyon Range (Pequera et al., 1994; Mitra et al., 1994; DeCelles et al., 1995), previous and recent studies in the San Pitch Mountains (also referred to as the Gunnison Plateau; Lawton, 1982, 1985, 1986; Lawton et al., 1993), and regional seismic and structural data (Standlee, 1982; Allmendinger et al., 1983, 1986; Royse, 1993; Coogan et al., 1995). Our results indicate that an overall eastward progression of frontal thrusting was accompanied by hindward thrust reactivation and growth of large structural culminations that profoundly influenced regional subsidence, sediment supply, and thrust-belt taper. GEOLOGIC AND STRUCTURAL SETTING A west-to-east transect through central Utah crosses several important Mesozoic and Cenozoic structures (Fig. 1). The Confusion Range synclinorium and House Range constitute a large synform-antiform pair that developed above a major thrust ramp in the hinterland of the Sevier belt (Hose, 1977; Allmendinger et al., 1983). Allmendinger et al. (1986) interpreted antiformal reflectors in basement rocks beneath the House Range as a large duplex produced during Sevier thrusting. East of the House Range lies the Sevier Desert basin, a large Tertiary basin underlain by the Sevier Desert detachment fault (McDonald, 1976; Allmendinger et al., 1983). Although the existence of the detachment beneath the southern Sevier Desert has been questioned (Anders and Christie-Blick, 1994), regional seismic and geologic data confirm its presence throughout the area discussed in this paper (Coogan et al., 1995). Restoration of 35 km of down-to-the-west displacement (Allmendinger et al., 1986) on the detachment brings the eastern limb of the basement duplex beneath the House Range to within a few kilometres of the Canyon Range. We refer to this broad antiform as Figure 1. Generalized geologic map of central Utah, after Hintze (1980). Inset shows location of map area in Utah. Boreholes: 1—Placid WXC Barton 1; 2—Placid WXC USA 1-2; 3—Cominco American #2 Beaver River. CRC indicates Canyon Range Conglomerate. Line A-A shows trace of regional geologic cross section (below), after Coogan et al. (1995). Major structures: CRT— Canyon Range thrust; PV—Pavant thrust; SDD—Sevier Desert detachment fault; PX—Paxton thrust; GUN—Gunnison thrust. Geology; August 1995; v. 23; no. 8; p. 699–702; 3 figures. 699 on January 29, 2010 geology.gsapubs. org Downloaded from