Anomalous cold in the Pangaean tropics: REPLY

Soreghan, Gerilyn S.; Soreghan, Michael J.; Poulsen, Christopher J.; Young, Roger A.; Eble, Cortland F.; Sweet, Dustin E.; Davogustto, Oswaldo

doi:10.1130/g30148y.1

Cited by 4 publications

(5 citation statements)

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“…In Soreghan et al (2008Soreghan et al ( , 2009aSoreghan et al ( , 2009bSoreghan et al ( , 2014, it was proposed that Unaweep Canyon was carved in the Permian-Pennsylvanian by upland glaciation when this region was at elevation atop the ancient Uncompahgre uplift, and that this paleolandscape was exhumed by late Cenozoic fl uvial action associated with drainage evolution across the northern Colorado Plateau of the upper Colorado River system. This hypothesis has been criticized, and remains controversial (for discussions and replies, see Soreghan et al, 2007Soreghan et al, , 2008Soreghan et al, , 2009aSoreghan et al, , 2009bAslan et al, 2008;Hood, 2009;Hood et al, 2009).…”

Section: Unaweep Canyonmentioning

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%

“…This hypothesis has been criticized, and remains controversial (for discussions and replies, see Soreghan et al, 2007Soreghan et al, , 2008Soreghan et al, , 2009aSoreghan et al, , 2009bAslan et al, 2008;Hood, 2009;Hood et al, 2009).…”

Section: Unaweep Canyonmentioning

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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“…(2007, 2008, 2014, 2015) posited formation by late Paleozoic glaciation, followed by Permian burial and Cenozoic partial exhumation by the ancestral Gunnison River. This hypothesis remains controversial (e.g., Hood, 2009; Hood et al., 2009; Soreghan et al., 2008; Soreghan, Soreghan, et al., 2009; Soreghan, Sweet, et al., 2009), since it implies low‐latitude and low‐elevation glaciation for the late Paleozoic, which is not a feature of current climate models for that time. The hypothesis hinges in part on observations that suggest a pre‐Mesozoic age for the landform (e.g., burial of Permian paleorelief) and inferred proglacial facies in the Permian fill, as well as a 320‐m core that mostly penetrated Pleistocene strata but ∼15 m of bas`al strata interpreted to date from the late Paleozoic based on palynological, provenance, and paleomagnetic data (Soreghan et al., 2008).…”

Section: Geologic Settingmentioning

confidence: 99%

Seismic Reflection and Electrical Resistivity Imaging Support Pre‐Quaternary Glaciation in the Rocky Mountains (Unaweep Canyon, Colorado)

Patterson

Behm

Chwatal

et al. 2021

Geophysical Research Letters

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Landscape shapes record processes of formation. In particular, fluvial processes typically exhibit V-shaped profiles with steep slopes, whereas glacial processes carve U-shaped valleys with variable slopes and overdeepenings (MacGregor et al., 2000;Prasicek et al., 2014). Overdeepened valleys are those with depths extending below fluvial base level (Preusser et al., 2010) and are key elements of glacial landscapes where warm-bed conditions exist(ed) (e.g., Benn & Evans, 1998;Cook & Swift, 2012). Such valleys are characterized by closed topographic depressions and are commonly eroded several hundred meters below the base level (Fiebig et al., 2010;Menzies, 1995;Preusser et al., 2010). Overdeepening on basement is unknown in canyons carved exclusively by fluvial processes (Cook & Swift, 2012;Huuse & Lykke-Andersen, 2000;Linton, 1963); rather, overdeepenings are considered "unambiguous features of glacially sculpted landscapes" (Pomper et al., 2017). Overdeepening occurs in cirques, valley outlets of alpine glaciers, and fjords and valleys draining continental ice sheets, related to perturbations in the bed that amplify the action of high-pressure meltwater (Hooke, 1991).Seismic imaging has been widely used to characterize Quaternary glacial valleys and, together with drilling and other subsurface data, has demonstrated the distinctive propensity for glacial processes to produce not Abstract Unaweep Canyon (Uncompahgre Plateau, Colorado) represents an enigmatic landscape with a complex evolution. Interpretations for its origin have ranged from ancestral fluvial erosion in the late Cenozoic to glacial erosion in the Paleozoic, or some combination thereof, with significant implications for global climatic and large-scale tectonic reconstructions. To address the conflicting interpretations, we acquired a high-resolution seismic reflection profile to investigate the depth, structure, and sedimentary infill in the canyon. The data set is further complemented with an electrical resistivity survey. Integrated with other geophysical and geological data, the results show an overdeepened Precambrian basement with transverse U shape and support the hypothesis of a pre-Quaternary glacial origin. Our data constitute the first detailed image of a buried pre-Quaternary glacial valley in North America; if substantiated with core studies, these results have far-reaching implications for our understanding of global ice houses as well as the tectonic conditions, enabling preservation of such systems. Plain Language SummaryThe shape of valleys depends on the processes that created them.Broad valleys with the transverse shape of a "U" are distinct signs of glaciers, which carved the valley in the bedrock. Since old valleys are filled up with sediments, we need geophysical tools to image their structure in the buried subsurface. Using such tools, we have found a buried U-shaped valley in western Colorado. Since we know from other observations that there were no glaciers in this specific location in the last ice age, the valley must have ...

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Anomalous cold in the Pangaean tropics: REPLY

Cited by 4 publications

References 5 publications

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

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

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

Seismic Reflection and Electrical Resistivity Imaging Support Pre‐Quaternary Glaciation in the Rocky Mountains (Unaweep Canyon, Colorado)

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