Chapter 23: Reconstruction of extensionally dismembered early Mesozoic sedimentary basins; Southwestern Colorado Plateau to the eastern Mojave Desert

Abstract

On the Colorado Plateau of southwestern Utah, the Lower Jurassic Glen CanyonGroup comprises, in ascending order, the Moenave and Kayenta Formations and the Navajo Sandstone. In southern Nevada and southeastern California, the lithostratigraphic equivalent of the Navajo Sandstone is the Aztec Sandstone. In southern Nevada, the Aztec Sandstone is conformably underlain by four informally recognized stratigraphic units (A-D) of the undifferentiated Moenave and Kayenta Formations. The Glen Canyon Group unconformably overlies the Upper Triassic Chinle Formation above a regional unconformity. In addition to the Petrified Forest and Shinarump Members, the Chinle Formation contains a distinctive limestone-pebble conglomerate at its base.Using the Aztec Sandstone as a distinctive reference unit, the Glen Canyon Group and its relation to underlying and overlying lower Mesozoic depositional sequences are traced southwestward from the Las Vegas extensional domain, along the eastern edge of the relatively unextended Las Vegas Range-Spring Mountains block, into the Jurassic arc terrane of the eastern Mojave Desert. Southwestward, the regional unconformity at the base of the Glen Canyon Group truncates progressively older strata into the arc terrane. Although Middle Jurassic strata have been erosionally or tectonically removed from the Las Vegas extensional basin, volcanic-clast-bearing marginal marine facies of the Middle Jurassic Carmel Formation are tentatively correlated with silicic volcanic, volcaniclastic, and epiclastic rocks of the southern end of the Spring Mountains extensional domain. Stratigraphic and facies boundaries in lower Mesozoic strata potentially serve as important strain markers to test models of Cenozoic extension. Restoration of structural blocks containing lower Mesozoic outcrops to their pre-Tertiary positions is based on restoration of the Las Vegas Range-Spring Mountains block to its preextension position. The reconstruction reveals that (1) the limestone-pebble conglomerate at the base of the Chinle Formation is truncated on the east by the north-south-trending VermilionCliffs paleovalley; (2) the undifferentiated Moenave and Kayenta Formations were deposited in a north-south-trending, incipient foreland basin that deepened to the north; (3) alluvial fans were shed northeastward, at right angles to the Triassic paleoslope, into this basin from the arc terrane; and (4) volcanic centers lying east of the present Colorado River served as the source of volcanic clasts in the Carmel Formation. Marzolf, J. E., 1990, Reconstruction of extensionally dismembered early Mesozoic sedimentary basins; Southwestern Colorado Plateau to the eastern Mojave Desert, in Wernicke, B. P., ed., Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada: Boulder, Colorado, Geological Society of America Memoir 176. 477 on June 20, 2015 memoirs.gsapubs.org Downloaded from 478 J. E. Marzolf w.Bounding Hurricane CliffsUnconformities J-2 J-1

Insights into North American Paleogeography and Paleotectonics from U–Pb ages of detrital zircons in Mesozoic strata of the Colorado Plateau, USA

“…Episodes of deflation within San Rafael ergs suggest that sand may have been blown only intermittently from the erg interior to the flank of the arc, with no continuous eolian sand blanket ever deposited across the intervening area (Dickinson and Gehrels 2009). Westward into California, discordant U-Pb ages for volcanic rocks enclosing eolianite lenses also suggest correlation of the latter with the San Rafael Group (Fackler-Adams et al 1997;Busby et al 2002), but stratigraphic mapping southward from the Colorado Plateau (Marzolf 1990) implies correlation of the California eolianite lenses with the Lower Jurassic Glen Canyon Group (Fig. 4a).…”

Extensional arc setting and ages of Middle Jurassic eolianites, Cowhole Mountains (eastern Mojave Desert block, California)

“…For other analytical details, see Mattinson (1994). also previously correlated with the Lower Jurassic Navajo Sandstone (Drewes, 1971;Bilodeau and Keith, 1986;Marzolf, 1990). Other intra-arc eolianites in Arizona and California, however, are age-equivalent to the Lower Jurassic Navajo and Wingate Sandstones (see discussion in Riggs et al, 1993).…”

“…Intra-arc eolianites in the Cowhole Mountains, previously correlated with backarc eolianites of the Lower Jurassic Navajo Sandstone (Marzolf, 1980(Marzolf, , 1990, are instead age equivalent to backarc eolianites of the Middle Jurassic Temple Cap and Carmel Formations dated by Kowalis et al (2001). They are also age equivalent to intra-arc eolianites in the Palen Mountains of southeastern California (Fackler-Adams et al, 1997), as well as intra-arc eolianites of the upper member of the Mount Wrightson Formation and the strata of Cobre Ridge in southern Arizona (Riggs et al, 1993).…”

Lower Mesozoic facies and crosscutting sequence boundaries: Constraints on displacement of the Caborca terrane

“…Distinctive quartzite-and chert-clast conglomerate overlain by variegated shale identify the Chinle Formation (Stewart et al, 1972a;Wilson and Stewart, 1967;Blakey and Middleton, 1983;Marzolf, 1990). Wilson and Stewart (1967) assigned redbeds unconformably overlying the Chinle Formation to the Moenave and Kayenta formations undivided.…”

“…This conclusion is supported by magnetostratigraphic data (Calderone and Beard, 1994). The Kayenta Formation intertongues with the overlying Aztec Sandstone (Wilson and Stewart, 1967;Blakey and Middleton, 1983;Marzolf, 1988bMarzolf, , 1990 The type locality of the Aztec Sandstone is Aztec Tank near Goodsprings, Nevada, (Hewett, 1931) near the southern end of the nearly continuous sandstone cliffs in the southern Spring Mountains. The Aztec Sandstone is unequivocally the lithostratigraphic equivalent of the Navajo Sandstone.…”