draft -- UNM PROFESSOR KARL KARLSTROM ON THE GRAND CANYON'S AGE -- draft

THE WEST END: DOES ITS YOUTH SETTLE AN OLD CONTROVERSY?

Following the paper trail of University of New Mexico Professor Karl E Karlstrom led me to some recent work that highlights the singular importance of the western Grand Canyon in wrestling with that most important of Grand Canyon chesnuts: How old is it? When did it take shape? Is it one big dig or a collection of ditches? 1964 saw elder geology statesman, E. McKee, take a lead in a significant symposium. Sixty years later, Dr. Karlstrom, an intimate and expert researcher and analyst of the Canyon, is leading the debate in marshaling the evidence for a young Canyon, and using, which is what interests me, data from the western end.

 The least-publicly known is the youngest geologically? Fascinating! There are several papers for the brave curious to search out. I have freely, but I hope not stupidly, cut and pasted pieces in order to focus in on the importance of the western end of the Grand Canyon as its youngest section and thus determiner of "how old" the Canyon is.

My inquiry brought this generous email from Dr. Karlstrom, (8 Jan 2024) summarizing recent relevant papers:

Feel free to post the abstracts and whatever is of interest from the published papers (see attached).

The 2014 "paleocanyon solution" Nature paper seems to have withstood an initial "test of time"--  one decade without any serious challenges is a good start. This paper highlighted westermost GC as a key testbed because, if it is "young" (carved in last 6 Ma), then so is the canyon as we see it today.

The 2017 paper added a nail by adding new thermochronology (cooling history) data.

A 2020 paper addressed another challenge to the young canyon model by showing that the Shinumo was not the likely source for old clasts found in S California deposits as proposed by others.

A 2021 paper refined the time of arrival of the Colorado River to the area just north of Needles about 5.2 Ma and to the Gulf of California between 4.8 and 4.63 Ma.

Western GC is one of my favorite sections as I did many Lower Gorge fieldcamp trips in the 1980s when I was teaching at NAU. The connections to the Hualapais are becoming increasingly important to highlight these days. I like to highlight the Hurricane and Grand wash fault systems as delineating the westernmost section and the end of GC and providing the main explanation for the lower elevation Hualpai plateau. (end of email)

                                  

My own long-running discussion (and promotion) of the Western Grand Canyon has concentrated on that area north of the Colorado from the distinctive dragon-head of the Westernmost High Point west to the northside butte near River Mile 277 (unnamed; I think of it as the Paiute Farewell Gatepost). On the map below (the Colorado shown as a red line), that area is bounded on the north by the light-green line. It is all within Grand Canyon National Park, and reachable through BLM lands and the Grand Canyon Parashant National Monument.

However, Dr. Karlstrom ends by mentioning the importance of the Hualapai lands and Plateau, south of the Colorado. I have, perhaps arbitrarily, marked off that southwest piece of the Canyon with the blue line. 

Arbitrarily only because unlike the federal lands north of the river, I have not, due to Hualapai Tribe rules, been able to visit south of the river except along the river's  shores. While names of plateaus like Kaibab, Shivwits, Coconino label well-known lands into which the Canyon is entrenched, that seems not true for the Hualapai Plateau. Indeed, as Dr. Karlstrom and the geology map down below indicate, south of the river, the geology does a different thing, not rising up to the heights of the Shivwits, but being of lower elevation with a broad exposure of Redwall limestone  (in purple): 

Even more obvious is how the classic stepped layers on the north contrast with Hualapai plateau's geological mixture. (Map, again, courtesy of https://rclark.github.io/grand-canyon-geology/.)  The map certainly does, as Dr. Karlstrom writes, highlight the Hurricane and Grand wash fault systems as delineating the westernmost section and the end of GC. The map below next shows how this section fits in with four other sections of Grand Canyon's "young (5-6 million years)" development hypothesis. To give flavor to the ongoing (150 years) discussion,  I have extracted a few quotes from two papers cited by Dr. Karlstrom: 

 "6 Ma age of carving Westernmost Grand Canyon,"  Earth and Planetary Science Letters  Volume 474, 15 September 2017, Pages 257-271

 The Age of Grand Canyon: Applying New Tests to Resolve the 150-year-old Debate                       URL: https://app.dimensions.ai/details/grant/grant.3582458    2014-05-01 to 2017-04-30   Grant 1348007; Directorate for Geosciences (Alexandria, US). 

Questions about the age of Grand Canyon, framed by John Wesley Powell in the late 1800s, address the tectonic and landscape evolution of the Grand Canyon region and the tectonic events that have shaped it. Recent papers reinvigorate the debate, and support models for both "old" (70-17 million years) and "young" (5-6 million years) carving of Grand Canyon, with corresponding tectonic models for "old" versus "young" uplift of the Colorado Plateau. 

Studies supporting the "old" canyon model suggest that an 80-70 million year old east-flowing river, then a 55-30 million year old west-flowing river, incised a canyon in the same location and to nearly the same depth as modern Grand Canyon. In this model, the Colorado River did not play a significant role in excavating Grand Canyon, and the preponderance of tectonic uplift of the Colorado Plateau took place about 70 million years ago. 

In contrast, "young" canyon models suggest that most of the Grand Canyon has been carved in the last 6 million years once the Colorado River became integrated from the Rocky Mountains to the Gulf of California and that uplift of the Colorado Plateau region has taken place in multiple episodes and may be ongoing due to regional mantle upwelling. 

This project tests a "paleocanyon resolution" for the Grand Canyon debate in which there are 3 "young" segments, 1 "old" segment, and 1 "intermediate" age segment that collectively provide a record of a complex multi-stage tectonic uplift history for the southwestern U.S. 

A map to illustrate the five segments of Grand Canyon carving:

In more detail:

A palaeocanyon solution for the age of the Grand Canyon:

Combined geological and thermochronological data indicate

that the Hurricane fault segment of Grand Canyon is ‘old’ and

was carved to about half its modern depth by a north-flowing

palaeoriver 65–50 Ma, but this Hualapai palaeoriver did not carve

adjacent segments where river-level samples were buried by several

kilometres of rock from 70 to 50 Ma. Eastern Grand Canyon

segment is intermediate in age and was carved across the Kaibab

Uplift to within approximately half the depth of modern Grand

Canyon between 25 and 15 million years ago. However, it could

not have been linked to Marble Canyon, which was deeply buried,

or Westernmost Grand Canyon, where a western exit is precluded

by both geology and thermochronology; hence it probably flowed

northwest (Fig. 1). Our palaeocanyon solution for carving Grand

Canyon suggests that the 5–6 Ma Colorado River became integrated

through two young (<6 Ma) segments (Marble Canyon and West-

ernmost Grand Canyon), one 25–15 Ma segment (Eastern Grand

Canyon), and a >50 Ma Hurricane segment. After integration of the

Colorado River 5–6 million years ago, all segments were widened

and Grand Canyon was deepened during semi-steady river incision over the past 4 Ma at rates of 100–200 m Ma−1 (refs 8,34).

Two complementary methods are used to test this hypothesis. First, apatite triple dating (fission track, (U-Th)/He dating, and 4He/3He analyses) are applied to new samples from each segment to reconstruct cooling paths for rocks and decipher past (now-eroded) landscapes and fault displacements. Second, detrital zircon and sanidine dating of key preserved paleoriver remnants provide essential ground truth to calibrate the thermochronological investigations. 

More broadly, the project’s  significance and importance are enhanced by intense national and international public interest in the Grand Canyon region as one of Earth's iconic geologic features. The results of this project may change the current paradigm for the incision age of the Grand Canyon. Discussion and resolution of the century-long Grand Canyon debate illustrates the scientific method and progress of science. The project will have significant impacts on student training, increased diversity of the geoscience workforce, outreach to Native American tribes in the region, public informal science education, and increased collaborative progress among diverse geosciences communities. 

Here is an interactive map of the Canyon's geology for the west end, though hardly fine-grained enough to illustrate the work summarized. (Courtesy of https://rclark.github.io/grand-canyon-geology/#12.58/36.12051/-113.91967.) The western scarp for Canyon country is pretty clear, as is the river running through and out into the landscape (the greens) of younger rock.

A more detailed view of the research as it concerns the westernmost Canyon:

Earth and Planetary Science Letters Volume 474, 15 September 2017, Pages 257-271

6 Ma age of carving Westernmost Grand Canyon: Reconciling geologic data with combined AFT, (U–Th)/He, and 4He/3He thermochronologic data(Article)(Open Access)

Carmen Winn a,∗

Karl E. Karlstrom a,∗

David L. Shuster b,c

Shari Kelley d

Matthew Fox b,c,e

a Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA

b Department of Earth and Planetary Sciences, University of California, Berkeley, CA, USA

c Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA, USA

d New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM, USA

e Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom

Abstract

Conflicting hypotheses about the timing of carving of the Grand Canyon involve either a 70 Ma (“old”) or <6 Ma (“young”) Grand Canyon. 

This paper evaluates the controversial westernmost segment of the Grand Canyon where the following lines of published evidence firmly favor a “young” Canyon. 

1) North-derived Paleocene Hindu Fanglomerate was deposited across the present track of the westernmost Grand Canyon, which therefore was not present at ∼55 Ma. 

2) The 19 Ma Separation Point basalt is stranded between high relief side canyons feeding the main stem of the Colorado River and was emplaced before these tributaries and the main canyon were incised. 

3) Geomorphic constraints indicate that relief generation in tributaries and on plateaus adjacent to the westernmost Grand Canyon took place after 17 Ma. 

4) The late Miocene–Pliocene Muddy Creek Formation constraint shows that no river carrying far-traveled materials exited at the mouth of the Grand Canyon until after 6 Ma. 

Interpretations of previously-published low-temperature thermochronologic data conflict with these lines of evidence, but are reconciled in this paper via the integration of three methods of analyses on the same sample: apatite (U–Th)/He ages (AHe), 4He/3He thermochronometry (4He/3He), and apatite fission-track ages and lengths (AFT). HeFTy software was used to generate time–temperature (t–T) paths that predict all new and published 4He/3He, AHe, and AFT data to within assumed uncertainties. These t–T paths show cooling from ∼100 °C to 40–60 °C in the Laramide (70–50 Ma), long-term residence at 40–60 °C in the mid-Tertiary (50–10 Ma), and cooling to near-surface temperatures after 10 Ma, and thus support young incision of the westernmost Grand Canyon. 

A subset of AHe data, when interpreted alone (i.e. without 4He/3He or AFT data), are better predicted by t–T paths that cool to surface temperatures during the Laramide, consistent with an “old” Grand Canyon. However, the combined AFT, AHe, and 4He/3He analysis of a key sample from Separation Canyon can only be reconciled by a “young” Canyon. Additional new AFT (5 samples) and AHe data (3 samples) in several locations along the canyon corridor also support a “young” Canyon. 

This inconsistency, which mimics the overall controversy of the age of the Grand Canyon, is reconciled here by optimizing cooling paths so they are most consistent with multiple thermochronometers from the same rocks. To do this, we adjusted model parameters and uncertainties to account for uncertainty in the rate of radiation damage annealing in these apatites during sedimentary burial and the resulting variations in He retentivity. In westernmost Grand Canyon, peak burial conditions (temperature and duration) during the Laramide were likely insufficient to fully anneal radiation damage that accumulated during prolonged, near-surface residence since the Proterozoic. We conclude that application of multiple thermochronometers from common rocks reconciles conflicting thermochronologic interpretations and the data presented here are best explained by a “young” westernmost Grand Canyon. Samples spread along the river corridor also suggest the possibility of variable mid-Tertiary thermal histories beneath north-retreating cliffs. © 2017 Elsevier B.V.