Active salt deformation and rapid, transient incision along the Colorado River near Moab, Utah

Abstract

In certain settings, erosion is driven by and balanced with tectonic uplift, but the evolution of many landscapes is dominated by other factors such as geologic substrate, drainage history, and transient incision. The Colorado Plateau is an example where these controls are debated and where salt deformation is hypothesized to be locally active and driven by differential unloading, although this is unconfirmed and unquantified in most places. We use luminescence-dated Colorado River terraces upstream of Moab, Utah, to quantify rates of salt-driven subsidence and uplift at the local scale. Active deformation in the study area is also supported by patterns of concavity along tributary drainages crossing salt structures. Subsidence in Professor Valley at a time-averaged rate of~500 m/Myr (meters/million years) is superimposed upon rapid bedrock incision rates that increase from~600 to~900 m/Myr upstream through the study area. Such high rates are unexpected given the absence of sources of regional tectonic uplift here. Instead, the incision rate pattern across the greater area is consistent with a transient signal, perhaps still from ancient drainage integration through Grand Canyon far downstream, and then amplified by unloading at both the broad regional scale and at the local canyon scale.

Geomorphic and stratigraphic evidence of Quaternary diapiric activity enhanced by fluvial incision. Navarrés salt wall and graben system, SE Spain

“…Higher vertical displacement rates would be obtained computing the cumulative uplift across the full span of the diapir. These values are comparable with those estimated in other active salt structures located in stable continental regions, such us the Paradox Basin, Colorado Plateau, USA (0.5-0.6 mm/yr; Jochems and Pederson, 2015), salt domes of Texas (0.45 mm/yr; Jackson and Seni, 1983), northern Germany (Gorbelen salt dome, 0.1-0.5 mm/yr; Zirngast, 1996) or the Ebro Cenozoic Basin, Spain (~0.3 mm/yr; Lucha et al, 2012). Moreover, as expected, they are much lower than those reported in highly active and prominent diapirs such as Mount Sedom, Israel (5-8 mm/yr; Frumkin, 1996;Weinberger et al, 2006), some salt plugs of the Zagros Mountains (e.g., >4 mm/yr; Bruthans et al, 2010), or Jabal Al Milh diapir, Yemen (4.5 mm/yr;Davison et al, 1996), all in tectonically active regions.…”

“…This data suggests that differential loading induced by fluvial entrenchment contributes to enhance diapiric activity in the region. The amount of topographic relief in the grabens of the Caroch Massif region (Table 4) is comparable with those found in other areas where salt flows towards erosionally unloaded valley floors: Canyonlands section of the Colorado Plateau (Jochems and Pederson, 2015;Furuya et al, 2007 and references therein); salt anticlines in the Ebro Cenozoic Basin (Lucha et al, 2008a(Lucha et al, , b, 2012 and in the Pyrenees, Spain (Gutiérrez et al, 2015); the Ambal salt pillow in the Zagros Mountains (Gutiérrez and Lizaga, 2016); the grabens of Peracalç in the Pyrenees (Gutiérrez et al, 2012) (Table 1). Moreover, Warsitzka et al (2013) and Peel (2014) illustrate through scaled physical experiments and forward modelling, respectively, that very small amounts of differential loading can initiate salt flowage.…”

“…Jahani et al (2007) propose an evolutionary morphologic classification for the salt diapirs in the Eastern Fars Province of the Zagros Mountains: (1) circular domes above buried salt; (2) high-relief salt extrusions; (3) salt extrusions with salt glaciers and a fountain or summit dome above the feeding vent; (4) empty craters with insoluble residues. Diapiric rise, typically with marked spatial gradients, may be recorded by uplifted, upwarped and tilted geomorphic and stratigraphic markers such as fluvial terraces (Kirkham et al, 2002;Jochems and Pederson, 2015;Lucha et al, 2008aLucha et al, , b, 2012Gutiérrez et al, 2015), marine terraces (Bruthans et al, 2010) or sea-floor deposits (Lee et al, 1996).…”

“…Recently, Jochems and Pederson (2015) documented and OSL-dated deformed strath and fill terraces of the Colorado River in a section near Moab, Utah, where the river traverses perpendicularly several anticlines cored by salt walls of the Paradox salt formation. They identified a reach with thickened and subsided fill terraces (Professor Valley) and a section with uplifted strath terraces showing upstream tilting (Salt-Cache salt wall).…”

Dip, layer spacing, and incision rate controls on the formation of strike valleys, cuestas, and cliffbands in heterogeneous stratigraphy

“…Because the field-measurable terms of interlayer spacing and structural dip contribute to the variability of landforms, the relationship between landform and base-level fall is not as straightforward as in uniform substrates (Forte et al, 2016). In the example of the Colorado Plateau, the cliff and cuesta landforms developed during a time of significant documented spatial and temporal variability in downcutting rates (Darling et al, 2012;Jochems and Pederson, 2015). The most prominent transience in the fluvial networks is related to deep, late Cenozoic entrenchment of the trunk streams due to drainage integration through the Grand Canyon.…”