Anomalous cold in the Pangaean tropics: COMMENT

Hood, William C.; Cole, Rex D.; Aslan, Andres

doi:10.1130/g30035c.1

Geology

2009

DOI: 10.1130/g30035c.1

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Anomalous cold in the Pangaean tropics: COMMENT

William C. Hood¹,

Rex D. Cole²,

Andres Aslan³

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2009

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Cited by 7 publications

(13 citation statements)

References 4 publications

(6 reference statements)

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“…Regardless, Cenozoic glaciation here is inconsistent with its low elevation (Soreghan et al, 2007). Hood et al (2009) conclude by stressing their view of a Cenozoic age for the canyon, citing as evidence the infl uence of Laramide-age faults, and the "bowl-shaped" longitudinal profi le of the (bedrock) canyon. We cannot test the validity of these suppositions; no one knows the earliest ages of movement on any faults that may have infl uenced the canyon, and the longitudinal shape of the bedrock canyon is unknown because the basement location and relief is obscured by a fi ll now known to (locally) exceed 320 m depth and 2 km width (Soreghan et al, 2009).…”

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confidence: 80%

“…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. We initially proposed a late Paleozoic age for the diamictite in outcrop on the basis of (1) late Paleozoic palynofl ora, and (2) an exclusive Precambrian provenance, which contrasts with the presence of Paleozoic and Mesozoic palynofl ora and Mesozoic clasts in an overlying (Quaternary) unit.…”

mentioning

confidence: 91%

“…We thank W. Hood et al (2009) for their Comment on our Geology paper . We recognize that our hypothesis of episodic cold in the Pangaean tropics, which relies, in part, on our proposal of a late Paleozoic age and glacial origin for Unaweep Canyon, is radical.…”

mentioning

confidence: 98%

“…Hood et al ignore our paleomagnetic inclination data, yet these data indicate that sediments of the basal core acquired a low inclination the last time that Colorado lay at low paleolatitudes-during late Paleozoic time. Hood et al (2009) suggest that Mesozoic strata should thicken into Unaweep Canyon if the canyon fi lled partially with Mesozoic strata. Such thickening is not needed if, as we hypothesize, Unaweep Canyon was buried by late Paleozoic time.…”

mentioning

confidence: 99%

“…We appreciate the comments of Hood et al (2009), but fi nd that they stem from either misrepresentations or suppositions. Our hypothesis is testable.…”

mentioning

confidence: 99%

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Anomalous cold in the Pangaean tropics: REPLY

Soreghan

Poulsen

et al. 2009

Geology

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mentioning

confidence: 80%

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confidence: 91%

mentioning

confidence: 98%

mentioning

confidence: 99%

“…We appreciate the comments of Hood et al (2009), but fi nd that they stem from either misrepresentations or suppositions. Our hypothesis is testable.…”

mentioning

confidence: 99%

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Anomalous cold in the Pangaean tropics: REPLY

Soreghan

Poulsen

et al. 2009

Geology

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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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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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Anomalous cold in the Pangaean tropics: COMMENT

Cited by 7 publications

References 4 publications

Anomalous cold in the Pangaean tropics: REPLY

Anomalous cold in the Pangaean tropics: REPLY

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

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

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