Preliminary geologic map of the Wupatki NE quadrangle, Arizona

Haines, D. V.; Bowles, C. Gilbert

doi:10.3133/ofr76703

Cited by 2 publications

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“…Gravels overlie a bedrock strath 151 m above the modern river ( Fig. DR-1.4 [see footnote 1]; Haines and Bowles, 1976) giving a bedrock incision rate of 193 m/Ma, somewhat higher than the 160 m/Ma post-623 ka rate at the CR-LCR confluence. The Black Point flow age constrains the 122-152 m terraces (L-2B of to be ca.…”

Section: Lower and Central Lcrmentioning

confidence: 99%

“…This age corrects an earlier inaccurate K-Ar age of 2.43 Ma that was applied to the Black Point flow ; late Black Point surface) by several workers (e.g., Billingsley, 2001;Holm, 2001a). The Black Point flow originated in the San Francisco volcanic field and flowed into the LCR channel as evidenced by thick alluvial sediments encountered in a drill hole beneath the flow (section DR-1 [see footnote 1]; Haines and Bowles, 1976).…”

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Cenozoic incision history of the Little Colorado River: Its role in carving Grand Canyon and onset of rapid incision in the past ca. 2 Ma in the Colorado River System

et al. 2016

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This paper documents a multi-stage incision and denudation history for the Little Colorado River (LCR) region of the southwestern Colorado Plateau over the past 70 Ma. The first two pulses of denudation are documented by thermochronologic data. Differential Laramide cooling of samples on the Mogollon Rim suggests carving of 70-30 Ma paleotopography by N-and E-flowing rivers whose pathways were partly controlled by strike valleys at the base of retreating Cretaceous cliffs. A second pulse of denudation is documented by apatite (U-Th)/He dates and thermal history models that indicate a broad LCR paleovalley was incised 25-15 Ma by an LCR paleoriver that flowed northwest and carved an East Kaibab paleovalley across the Kaibab uplift. Lacustrine strata of the lower Bidahochi Formation were deposited 16-14 Ma in the LCR paleovalley in a closed basin playa or marsh with a valley center near the modern LCR. There is a hiatus in the depositional record in the LCR valley from 12 to 8 Ma followed by aggradation of the 8-6 Ma fluvial upper Bidahochi Formation. Interlayered 8-6 Ma maar basalts that interacted with groundwater mark local base level for upper Bidahochi fluvial deposits; this was also a time of increased groundwater flow to Hualapai Limestone at the western edge of the Colorado Plateau. The paleo-base level in the central LCR valley remained stable (~1900 m modern elevation) from 16 to 6 Ma. The third pulse of regional incision and denudation, most recent and ongoing, started after integration of the Colorado River (CR) through Grand Canyon. Thermochronology from Marble Canyon indicates that early CR integration took place across the Vermillion Cliffs at Lees Ferry after 6 Ma. The elevation of the paleoconfluence between the LCR and CR at 5-6 Ma is poorly constrained, but earliest CR integration is hypothesized to have reoccupied the East Kaibab paleocanyon. In the upper LCR drainage, topographically inverted basalt mesas have elevations and K-Ar dates indicating a transition from aggradation to incision ca. 6 Ma followed by semi-steady incision of 20-40 m/Ma. In the lower LCR, incision accelerated to 120-170 m/Ma after 2 Ma as indicated by 40 Ar/ 39 Ar dating of basalt, ash-fall, and detrital sanidine. A 1.993 ± 0.002 Ma sanidine age for a tuff in the White Mesa alluvium provides a breakthrough for LCR and CR incision studies. Post-2 Ma differential incision magnitudes (and rates) in the lower LCR and at the LCR-CR confluence were 280-320 m (140-160 m/Ma), about three times greater than the 40-80 m (20-40 m/Ma) in the LCR headwaters. The proposed mechanisms driving overall post-6 Ma differential incision of the LCR involve headwater uplift associated with the Hopi Buttes and Springer ville volcanic fields plus base-level fall caused by CR integration to the Gulf of California. A proposed mechanism to explain the accelerated post-2 Ma differential incision in the central and lower LCR valley, but not in the head waters, involves mantle-driven epeirogenic uplift due to NE-migrating vol canism associated with the...

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Section: Lower and Central Lcrmentioning

confidence: 99%

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confidence: 99%

Cenozoic incision history of the Little Colorado River: Its role in carving Grand Canyon and onset of rapid incision in the past ca. 2 Ma in the Colorado River System

et al. 2016

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Reevaluation of the Crooked Ridge River—Early Pleistocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern Arizona

et al. 2016

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Essential features of the previously named and described Miocene Crooked Ridge River in northeastern Arizona (USA) are reexamined using new geologic and geochronologic data. Previously it was proposed that Cenozoic alluvium at Crooked Ridge and southern White Mesa was pre-early Miocene, the product of a large, vigorous late Paleogene river draining the 35-23 Ma San Juan Mountains volcanic field of southwestern Colorado. The paleoriver probably breeched the Kaibab uplift and was considered important in the early evolution of the Colorado River and Grand Canyon. In this paper, we reexamine the character and age of these Cenozoic deposits. The alluvial record originally used to propose the hypothetical paleoriver is best exposed on White Mesa, providing the informal name White Mesa alluvium. The alluvium is 20-50 m thick and is in the bedrock-bound White Mesa paleovalley system, which comprises 5 tributary paleochannels. Gravel composition, detrital zircon data, and paleochannel orientation indicate that sediment originated mainly from local Cretaceous bedrock north, northeast, and south of White Mesa. Sedimentologic and fossil evidence imply alluviation in a low-energy suspended sediment fluvial system with abundant fine-grained overbank deposits, indicating a local channel system rather than a vigorous braided river with distant headwaters. The alluvium contains exotic gravel clasts of Proterozoic basement and rare Oligocene volcanic clasts as well as Oligocene-Miocene detrital sanidine related to multiple caldera eruptions of the San Juan Mountains and elsewhere. These exotic clasts and sanidine likely came from ancient rivers draining the San Juan Mountains. However, in this paper we show that the White Mesa alluvium is early Pleistocene (ca. 2 Ma) rather than pre-early Miocene. Combined 40 Ar/ 39 Ar dating of an interbedded tuff and detrital sanidine ages show that the basal White Mesa alluvium was deposited at 1.993 ± 0.002 Ma, consistent with a detrital sanidine maximum depositional age of 2.02 ± 0.02 Ma. Geomorphic relations show that the White Mesa alluvium is older than inset gravels that are interbedded with 1.2-0.8 Ma Bishop-Glass Mountain tuff. The new ca. 2 Ma age for the White Mesa alluvium refutes the hypothesis of a large regional Miocene(?) Crooked Ridge paleoriver that predated carving of the Grand Canyon. Instead, White Mesa paleodrainage was the northernmost extension of the ancestral Little Colorado River drainage basin. This finding is important for understanding Colorado River evolution because it provides a datum for quantifying rapid post-2 Ma regional denudation of the Grand Canyon region.

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Preliminary geologic map of the Wupatki NE quadrangle, Arizona

Cited by 2 publications

References 1 publication

Cenozoic incision history of the Little Colorado River: Its role in carving Grand Canyon and onset of rapid incision in the past ca. 2 Ma in the Colorado River System

Cenozoic incision history of the Little Colorado River: Its role in carving Grand Canyon and onset of rapid incision in the past ca. 2 Ma in the Colorado River System

Reevaluation of the Crooked Ridge River—Early Pleistocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern Arizona

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