Growth faults in the Kaiparowits Basin, Utah, pinpoint initial Laramide deformation in the western Colorado Plateau

Abstract

Growth faults and synorogenic sedimentary strata preserved in Upper Cretaceous units on the margin of the Kaiparowits Basin in southern Utah pinpoint the timing of onset of the Laramide orogeny in this region between 80 and 76 Ma. The newly identifi ed listric normal faults, exposed in the steep limb of the East Kaibab monocline, sole into shales and evaporites of the Jurassic Carmel Formation. Faults lose displacement up-section through the Cretaceous Wahweap Formation and are associated with numerous coseismic sedimentary features. Fault orientations and slip vectors yield strain directions consistent with fold-related extension parallel to the axis of the growing East Kaibab monocline, or with development of a pull-apart basin at a bend in the trend of the fold. The association of the faults with the steep limb of a major basement-cored structure links them to initial Laramide movement along the Kaibab Uplift. When combined with recent radiometric ages of rock units bracketing the fault-induced growth strata, these sedimentary and structural features narrowly defi ne the onset of Laramide deformation in the western Colorado Plateau.

Correlation and Provenance of Upper Cretaceous (Campanian) Fluvial Strata, Utah, U.S.A., from Zircon U-Pb Geochronology and Petrography

“…Short-dash regression line indicates interpolated stratigraphic age from bentonites (equals uncompacted sedimentation rate of 400 m/My). Long-dash regression line indicates estimated bentonite age shift that results from use of 40 K decay constant of Kuiper et al (2008). southeastward paleocurrents during deposition of this suite indicates that Laramide uplifts, which had begun to form during deposition of the capping sandstone member (Tindall et al 2010), exercised increasing influence on foreland drainage patterns (Roberts 2007). Development of incipient Laramide topography in the former foreland basin may have shielded Kaiparowits rivers from thrust-belt-derived detritus.…”

“…Laramide deformation, with a distinctive basementinvolved structural style, was likely caused by flat-slab subduction of the Farallon plate beneath the North American plate (Dickinson and Snyder 1978;Miller et al 1992;Saleeby 2003). Initial Laramide deformation on the southwestern flank of the Kaiparowits Basin is inferred to have begun between 80 and 76 Ma, recorded by growth faults in middle Campanian strata (capping sandstone member of the Wahweap Formation) directly beneath the Kaiparowits Formation (Tindall et al 2010); the faults are interpreted as kinematically linked to initial folding on the East Kaibab monocline, which forms the eastern structural boundary of the Kaibab uplift ( Fig. 1).…”

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“…Growth faults along the East Kaibab monocline fl anking the Kaibab uplift bracket the onset of Laramide deformation at 80-76 Ma (Tindall et al, 2010) in middle Campanian time and thinning of Cretaceous strata across the San Rafael Swell farther north document initiation of that uplift as a subsurface growth fold as early as 77 Ma (Aschoff and Steel, 2011) within the same time frame. Initiation of the uplifts as buried subsurface structures did not initially preclude transport of sediment across their evolving crests, but the unconformity between the Kaiparowits Formation and the Canaan Peak Formation in the Table Cliff syncline implies that the Kaibab uplift had attained surfi cial relief by Maastrichtian time.…”

“…15). A potential means for recycling Kaiparowits sand into younger units during Laramide deformation is to posit removal of Kaiparowits strata from the crest of the Kaibab uplift, which displays 1.6 km of structural relief adjacent to the Table Cliff syncline (Tindall et al, 2010).…”

Rejection of the lake spillover model for initial incision of the Grand Canyon, and discussion of alternatives

“…Growth faults displacing units as young as the middle Campanian Wahweap Formation(Tindall et al, 2010) along the East Kaibab monocline show that deformation was under way by 80-78 Ma(Fig. 3A).…”