An Exhumed Late Paleozoic Canyon in the Rocky Mountains: A Discussion

Hood, William C.

doi:10.1086/595789

Cited by 11 publications

(17 citation statements)

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“…On the basis of cosmo genic dating (Balco et al, 2013), the upper three units are of Pleistocene age. In Soreghan et al (2007) a late Paleozoic age was posited for the basal unit, but this hypothesis remains contested (Aslan et al, 2008Hood, 2009;Hood et al, 2009). (For additional details of methods and results of coring, see Marra, 2008.…”

Section: Unaweep Canyonmentioning

confidence: 99%

“…Soreghan et al (2007) proposed a late Paleozoic age for the Precambrian-hosted inner gorge of Unaweep Canyon; Soreghan et al (2008Soreghan et al ( , 2014 further suggested an initial (Paleozoic) glacial origin followed by Cenozoic fl uvial exhumation of the ancient valley. Both the Paleozoic age and glacial origin remain controversial (Aslan et al, 2008Hood, 2009;Hood et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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Geology of Unaweep Canyon and its role in the drainage evolution of the northern Colorado Plateau

et al. 2015

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Unaweep Canyon (Colorado, USA) is a large, Precambrian-cored gorge that bisects the Uncompahgre Plateau of the northeastern Colorado Plateau, but has no through-fl owing axial stream; it is drained by two underfi t creeks (East and WestCreek) that head at a divide within the canyon. The history of the canyon and its role in drainage evolution of the Colorado River system remain controversial. New mapping of both bedrock and Quaternary units as well as analyses of Quaternary deposits in and near the canyon shed light on its late Cenozoic history, and call into question whether the canyon was incised by a Cenozoic river, or merely exhumed by one. Gravels near the western mouth of Unaweep Canyon (Gateway, Colorado) exhibit a distinctive intermediate volcanic provenance recording the presence of an ancestral Gunnison River; the youngest gravels are dated to 1.46 ± 0.33 Ma. Previously documented coring within the canyon reveals a thick (locally >330 m) fi ll that includes a lacustrine succession (~140 m thick), dated to 1.4-1.3 Ma, overlain by stacked paleosols and a thick (~160 m) conglomeratic unit emplaced between 1.3 Ma and the present, in addition to a basal unit of possible late Paleozoic age. Lake formation refl ects catastrophic mass wasting in western Unaweep Canyon that blocked the ancestral Gunnison River, causing partial backfi lling of the canyon, and forcing the river to seek a lower elevation exit eastward by breaching the Mesozoic rim at the northeast end of Cactus Park (Mesa County, Colorado). Ultimately, the ancestral Gunnison River joined the lower elevation Colorado River near Grand Junction by 1.3 Ma, incising the East Creek of Unaweep Canyon during the overspilling event. Thermochronological data from Precambrian basement within Unaweep Canyon and Permian strata at the western mouth of the canyon indicate onset of incision in latest Miocene time (ca. 6-5 Ma), at a timeaveraged rate of ~210-275 m/m.y. Onset of canyon occupation and rapid incision by the ancestral Gunnison River coincided with the timing of integration of the lower Colorado River system to the Gulf of California. The synchroneity of this incision across the Colorado Plateau supports the inference of an ultimate tectonic or epeirorogenic driver for this widespread incision and ultimate drainage integration.Several aspects of this data set support the previously published hypothesis that the ancestral Gunnison River exhumed a paleovalley. New mapping at the western mouth of the canyon documents a paleovalley fi lled with Permian strata that leads into the modern Precambrian-hosted gorge of Unaweep Canyon. In addition, the ancestral Gunnison River paralleled the Uncompahgre Plateau before making a 90° turn to bisect the structural axis in a manner that opposes both the northwestward plunge of the uplift and the northeastward dip of its northern fl ank. The rate of incision of Unaweep Canyon exceeds regional time-averaged incision rates, consistent with removal of sedimentary fi ll rather than incision of crystalline basement. This hyp...

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Section: Unaweep Canyonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Geology of Unaweep Canyon and its role in the drainage evolution of the northern Colorado Plateau

et al. 2015

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“…Subsequent investigators have sided with either the Colorado River argument (Cater, 1955;Hunt, 1956Hunt, , 1969Lohman, 1961Lohman, , 1965Lohman, , 1981Yeend, 1969;Betton et al, 2005;Scott et al, 2001Scott et al, , 2002aSteven, 2002;Hood et al, 2002;Hood, 2011) or the Gunnison River interpretation (Dane, 1935;Cater, 1966;Sinnock, 1978Sinnock, , 1981Perry, 1989;Perry and Annis, 1990;Perry and Young, 2003;Kaplan et al, 2005;Kaplan, 2006;Soreghan et al, 2007;Marra et al, 2010). A more recent controversy involves whether the canyon existed in late Paleozoic time (Soreghan et al, 2007(Soreghan et al, , 2009a(Soreghan et al, , 2009bHood, 2009;Hood et al, 2009). However, this controversy has no bearing on the abandonment of Unaweep Canyon.…”

Section: Origin Of Unaweep Canyonmentioning

confidence: 99%

Aftermath of a stream capture: Cactus Park lake spillover and the origin of East Creek, Uncompahgre Plateau, western Colorado

2014

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Newly discovered lacustrine strata suggest that the most signifi cant episode of stream capture in the upper Colorado River system (western USA), namely the abandonment of Unaweep Canyon, probably involved a combination of headward erosion and lake spillover. The abandonment of Unaweep Canyon occurred in two stages. The fi rst stage was marked by the capture of the Colorado River, after which time the Gunnison River continued to incise. Continued incision by the Gunnison River created a wall of rock on the east side of the Gunnison River valley in Cactus Park and left the abandoned Colorado River bed well above the Gunnison River. The second stage involved two blockages, one created by the thick fi ll within Unaweep Canyon and one at the south end of Cactus Park, which led to the creation of a lake within Cactus Park. The lake level rose until it fl ooded the abandoned Colorado River bed and spilled over at the point where the Colorado River had been captured earlier, during the fi rst stage of abandonment. Present-day East Creek was created by re-incision of the abandoned Colorado River course, which explains why the course of East Creek has a northeastward trend that is completely anomalous with respect to all other tributaries draining this area of the Uncom pahgre Plateau. The rapid incision created a large quantity of debris that defl ected the Gunnison River eastward at the mouth of East Creek. The evidence suggests that the abandonment of Cactus Park and Unaweep Canyon by the Gunnison River and the creation and destruction of Cactus Park lake all likely occurred ca. 800 ka and shortly thereafter. The Unaweep Canyon classic example of stream piracy illustrates how piracy alone can dramatically infl uence landscape development even in the absence of signifi cant tectonic and climatic infl uences.

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“…Hence, scrutiny of our data and reasoning is justifi ed. Note that we addressed several of Hood's arguments about the canyon age in a separate Reply to a Discussion of Soreghan et al (2007) (Soreghan et al, 2009;Hood, 2009). Hood et al (2009) question the age of diamictite found in an outcrop and core within Unaweep Canyon.…”

mentioning

confidence: 91%

“…This is an interesting departure from Hood (2009), who attempted to refute a glacial origin for these strata, preferring an origin as a talus deposit. Regardless, Cenozoic glaciation here is inconsistent with its low elevation (Soreghan et al, 2007).…”

mentioning

confidence: 94%