Comment on "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems"

Pederson, Joel L.; Young, R. A.; Lucchitta, Ivo; Beard, Les P.; Billingsley, George H.

doi:10.1126/science.1158019

Cited by 12 publications

(11 citation statements)

References 8 publications

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“…These results show that it is geomorphically possible for a paleodrainage of the size proposed by Young (2008) to capture an ancestral Colorado River east of the Shivwitz Plateau and west of Muav Gorge. As noted in the Introduction, however, most experts on the geology of this region agree that the limited volume of clastic debris deposited in the Grand Wash Trough and adjacent basins between 16.5 and 6 Ma rules out this hypothesis (e.g., Pederson et al, 2008).…”

Section: Constraints On Models For Colorado River Integrationmentioning

confidence: 94%

“…The depth and width of that incisional response to offset is not well constrained, but speleothem records of groundwater-table elevations in western Grand Canyon suggest that a proto-Grand Canyon began carving down to the level of the Redwall Limestone at 16 Ma (Hill et al, 2001;Polyak et al, 2008). The speleo them records are controversial, however, because groundwater tables in western Grand Canyon could have lowered due to offset along the Grand Wash-Wheeler Fault system rather than by incision in western Grand Canyon (Pearthree et al, 2008;Pederson et al, 2008). Sediments of the Muddy Creek Formation indicate that the upper Colorado River was not integrated with the Grand Wash Trough until 5.5-6 Ma (Spencer et al, 1998;Faulds et al, 2001).…”

Section: Introductionmentioning

confidence: 95%

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Numerical modeling of the late Cenozoic geomorphic evolution of Grand Canyon, Arizona

Pelletier

2009

Geological Society of America Bulletin

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The late Cenozoic geomorphic evolution of Grand Canyon has been infl uenced by three primary tectonic and drainage adjustment events. First, 1 km of relief was produced along the Grand Wash-Wheeler Fault system beginning at 16.5 Ma. Second, the ancestral Colorado River became integrated with the lower Colorado River through Grand Canyon between 5.5 and 6 Ma. Third, the Colorado River was infl uenced by Plio-Quaternary normal faulting along the Hurri cane and Toroweap Faults. Despite the relatively fi rm constraints available on the timing of these events, the geomorphic evolution of Grand Canyon is still not well constrained. For example, was there a deeply incised gorge in western Grand Canyon before Colorado River integration? How did incision rates vary through time and along the evolving river profi le? What is the role of isostatic rebound and Plio-Quaternary faulting on the recent incision history of Grand Canyon? In this paper I describe the results of a process-based numerical modeling study designed to address these questions and to determine the plausibility of different proposed models for the erosional history of Grand Canyon. The numerical model I developed integrates the stream-power model for bedrock channel erosion with cliff retreat and the fl exural-isostatic response to erosion. Two end-member paleodrainage and integration scenarios are considered. In the fi rst model, I assume no incision in western Grand Canyon prior to 6 Ma. This model is equivalent to a lake-overtopping scenario for Colorado River integration. In this scenario, the model predicts that Colorado River integration at 6 Ma initiated the formation of a large (700 m) knickpoint that migrated headward at a rate of 100 km/Ma, resulting in rapid incision of western Grand Canyon down to the level of the Redwall Limestone from 6 to 4 Ma and incision of eastern Grand and Marble Canyons from 4 to 2 Ma. Widening of Grand Canyon by cliff retreat triggered fl exural-isostatic rebound and renewed river incision of up to 350 m in Plio-Quaternary time according to this model. The model also indicates that Plio-Quaternary normal faulting signifi cantly dampened incision rates in western Grand Canyon relative to eastern Grand Canyon. In the second paleodrainage scenario, I assume that a 13,000 km 2 paleodrainage crossed the Grand Wash-Wheeler Fault system at 16.5 Ma. The results of this model scenario indicate that relief production along the Grand Wash-Wheeler Fault system could have initiated the formation of a large (700 m) knickpoint that migrated headward at a rate of 15 km/Ma prior to 6 Ma to form a 150-km-long gorge in western Grand Canyon. Following integration at 6 Ma, the results of this model scenario are broadly similar to those of the fi rst model, i.e., rapid incision through Grand and Marble Canyons from 6 to 2 Ma followed by cliff retreat, isostatic rebound, and fault-controlled incision. The results of the second model scenario illus trate that headward erosion of a protoGrand Canyon could have been suffi cient to capture the a...

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Section: Constraints On Models For Colorado River Integrationmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 95%

Numerical modeling of the late Cenozoic geomorphic evolution of Grand Canyon, Arizona

Pelletier

2009

Geological Society of America Bulletin

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“…Pederson et al (2) and Pearthree et al (3) raise a number of concerns about our analysis, which we address here. We recognize that some of the controversy generated by our paper relates to the definition of the Grand Canyon.…”

mentioning

confidence: 92%

“…Pederson et al (2) argue that an older western Grand Canyon contradicts long-established regional knowledge. Although it is true that this concept does contradict pre-early 1990s knowledge, it does not contradict more recent findings (7)(8)(9)(10)(11)(12), including a paper on the pre-Colorado River drainage in the Western Grand Canyon (5).…”

mentioning

confidence: 99%

“…We would first like to address the objection made by both Pederson et al (2) and Pearthree et al (3) to the so-called "Muddy Creek" problem, which involves the relative lack of siliciclastic sediment in the 16-to 6-million-year-old Muddy Creek Formation at the mouth of the Grand Canyon. Sediment should seemingly exist in this region if there was a "precursor" western Grand Canyon before 6 Ma that extended from the Grand Wash Cliffs to the west side of the Kaibab arch.…”

mentioning

confidence: 99%

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Response to Comments on the "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems"

Polyak

Hill

Asmerom

2008

Science

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Pederson et al . and Pearthree et al . offer critical comments on our study of the age and evolution of the Grand Canyon. Both sets of authors question our use of incision rates from two sample sites located outside the canyon and present alternative interpretations of our data. As we explain, even without the sites in question, our data support a “precursor” western Grand Canyon older than 6 million years.

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References

2012

Speleothem Science

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Comment on "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems"

Cited by 12 publications

References 8 publications

Numerical modeling of the late Cenozoic geomorphic evolution of Grand Canyon, Arizona

Numerical modeling of the late Cenozoic geomorphic evolution of Grand Canyon, Arizona

Response to Comments on the "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems"

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