Grand Canyon Unconformities and Deep Time – Part 1

by | Dec 24, 2024 | Age of the Earth, Geology and the Flood, Jesus and Science

PDF file available here

Are there “incontrovertible” reasons to affirm a young Earth? What does it mean to be incontrovertible?  Some YEC seem to believe that this means that it is claimed by any YEC author that they appreciate.  It is easy to list claims that might sound impressive.  What happens if we dig into those claims?  Can they stand up to analysis?

Geologists interpret the tremendous amount of sedimentary rocks on the Earth to have been deposited over billions of years.  That is a big disconnect with YEC claims that the Earth is 6,000 years old.  Such sediment accumulations are often miles thick.  The thickest sediments preserved today in the Grand Canyon at any one spot is 5000 ft (1500 m) thick. Much thicker sediment columns are found in other places.  Geologists don’t believe that the sediments were laid down continuously but that there were periods of erosion and non-deposition.  Some YEC are skeptical of the Grand Canyon unconformities.  Several examples are questioned.  Are these unconformities bogus or perhaps just part a global flood deposit. Let’s look at the claims. This is another one the “incontrovertible” evidences from Paul Humber’s “Reasons to Affirm a Young Earth”.  (Humber 2013)

The reason given in this case is:

18.   “Two very distinct, Grand Canyon unconformities”

Part 1

 

This reason from Humber’s booklet again actually involves two different issues, so I will use two separate discussions to cover them.  This is Part 1.  First, we can look at the observation from nature and then the assertions that Humber makes regarding them. 

Observation 1:  Unconformities are recognized in the Grand Canyon and it is the consensus of geologists that along some of these surfaces, millions of years of time are missing. 

Assertions:

  1. The evidence for the amount of time missing being millions of years between the layers above and below the unconformities is inadequate (miniscule).

 2.  Our experience regarding how much erosion takes place in a few years tells us that these unconformities could not represent millions or billions of years.

For clarity, geologists recognize an unconformity as the surface that separates older rocks from younger rocks where there is time not represented by rock deposition.  In an ultimate sense, even the base of a tidal cycle is a tiny unconformity.  The surfaces that are considered here are much more extensive.

Humber uses two unconformities in the Grand Canyon as examples of this.

  1. The Coconino-Hermit contact
  2. The Great Unconformity, expressed in the Grand Canyon at the base of the Tapeats Sandstone.

Do these unconformities support his assertions?  Part 1 will deal with the first of these:

Does Flood Geology explain the rocks in the Grand Canyon?

  1. The Coconino-Hermit contact

This is normally characterized as a disconformity because the beds above and below the unconformity surface are relatively parallel.  Some truncation is recognized as shown in a photograph from page 98 in the book, “The Grand Canyon: Monument to an Ancient Earth”. (Hill et al. 2016).  The discussion of issue 17 is relevant to this surface because surface could be described as smooth. (Flat Rocks, Unconformities and Deep Time (Part 1)). Both the Coconino and Hermit formations are Permian period in age (regardless of what that absolute age is).  In some parts of the Colorado Plateau, another formation, the Schnebly Hill Formation comes between them. (Bills, Flynn, and Monroe 2007)   The contact between the Schnebly Hill formation and the Hermit Shale is an unconformity (Figure 1)  The contact between Schnebly Hill Fm and the Coconino is interpreted as gradational. The recognition that in other parts of the Colorado Plateau, another formation exists that is missing in the Grand Canyon supports the interpretation of an unconformity at the boundary between the Coconino and Hermit formations.  Thus we can be sure that a break of some duration took place between the two formations.  How would we know how long it was?  No one claims that this was a major unconformity. YEC author, Roth did not break it out as a significant unconformity in his chronostratigraphic cross-section of the Grand Canyon.  (Roth 2009)

Figure 1 Stratigraphic column from Bills, Flynn, and Monroe (2007)

 Knowing specifically how much time is missing between the units would require knowing the age of the Coconino where it sets unconformably over the Hermit, and the age of the Hermit that remained after the erosion. 

Wearing down mountains?

The age of the three formations according to the sources that I found is as follows:

          Coconino Sandstone:  275–282 million years old

          Schnebly Hill Formation:  273-286 million years old

          Hermit Shale:  285 million years old

These are age estimates from different interpreters.  None of these units inherently have minerals that were formed at the time of deposition that can be dated radiometrically.  Assigning an age in millions of years involves correlating the formations to rocks that can actually be dated radiometrically.  No one has a direct method of dating these particular formations and there will remain uncertainty. Note that YEC do not have any method of directly dating these or other rocks in ways that fit their age interpretations.

A reasonable explanation for what we observe here suggested by the formations can be summarized this way:

  1. First the Hermit shale was deposited in a semi-arid to arid climate with many small channels over a low lying coastal plain (Blakey 1990).
  2. A period of erosion took place that beveled off an unknown amount of the Hermit.
  3. In at least eastern and central Arizona, the red flat lying sandstones of the Schnebly Hill Formation were deposited, primarily by wind processes. Gradually the dune deposits of the Coconino Formation expanded over the area, covering the exposed Hermit Shale. (Middleton, Elliott, and Morales 1990; Helble 2024)

In this scenario, and using the date estimates from before, there is still uncertainty in how much gap existed between these two formations.  Add to this the fact that, as Graham, 2020 observed, “Poor exposures, a fine-grained texture, and general lack of interesting features make the overlying, slope forming Hermit Shale (Ph) one of the least studied units in the Grand Canyon.”  (Graham 2020) Between the time transgressive nature of the units and contacts and the lack of contemporaneous igneous activity to use to date the units, the time missing in the rocks is uncertain and varies across the area.  There could have been a small gap, up to a few million years difference between the local age of the rocks below the unconformity and those above it.  The erosion itself might have taken place quickly in geologic terms.

Now to circle back to the assertions that Humber made, regarding this relatively small unconformity.

  1. The evidence for the time not represented being millions of years took place between the layers above and below it is inadequate (miniscule).

Geologists do not claim to know exactly how long it took to develop the unconformity or how much erosion took place vs. non-deposition. That said, there is no data to suggest that it could have been short enough to fit in flood geology timelines. Proposed YEC interpretations would mean that the deposition of the formations and the erosion would have taken place in a few days.  That is just a conjecture based on one particular interpretation of Genesis.  The depositional evidence for the Coconino Sandstone argues against a flood interpretation.

  1. Our experience regarding how much erosion takes place in a few years tells that these unconformities could not represent millions or billions of years.

Does human experience provide a good guide for how long geological processes require?  This sounds a bit like circular logic.  More on this in the next part, regarding the second unconformity.

References Cited:

Bills, Donald J., Marilyn E. Flynn, and Stephen A. Monroe. 2007. “Hydrogeology of the Coconino Plateau and Adjacent Areas, Coconino and Yavapai Counties, Arizona.” 2005–5222. Scientific Investigations Report. U.S. Geological Survey. https://doi.org/10.3133/sir20055222.

Blakey, Ronald C. 1990. “Supai Group and Hermit Formation.” In Grand Canyon Geology, 147–82. Oxford University Press.

Graham, John P. 2020. “Grand Canyon National Park Geologic Resources Inventory Report.” Natural Resource Report NPS/NRSS/GRD/NRR—2020/2195. National Park Service.

Helble, Timothy. 2024. “Flood Geology and Conventional Geology Face Off Over the Coconino Sandstone.” Perspectives on Science and Christian Faith 76 (2): 86–106. https://doi.org/10.56315/PSCF9-24Helble.

Hill, Carol, Gregg Davidson, Wayne Ranney, and Tim Helble, eds. 2016. The Grand Canyon, Monument to an Ancient Earth: Can Noah’s Flood Explain the Grand Canyon? Grand Rapids, MI: Kregel Publications.

Humber, Paul G. 2013. Reasons to Affirm a Young Earth. Vol. e-book revision. https://static1.squarespace.com/static/54235fb7e4b0dab08d8d81dd/t/57d6e6b3d482e999611d7888/1473701556828/ReasonsAffirmYE+CRS+e-book.pdf?fbclid=IwZXh0bgNhZW0CMTAAAR0J_JCi_6zH1KuNlHYrgIJjTAhCgOm4zwio8ks44k5CGnJIAiETnqThXLI_aem_BA94GfB1gm5q86tQj_pW2w.

Karlstrom, Karl E. 2019. “Parsing Grand Canyon’s Great Unconformity– Composite Erosion Surface From at Least Three Episodes Between 1,350 and 508 MA.” In . GSA. https://gsa.confex.com/gsa/2019AM/webprogram/Paper332195.html.

Middleton, Larry T., David K. Elliott, and Michael Morales. 1990. “Chapter 10 Coconino Sandstone.” In Grand Canyon Geology.

Pevehouse, Katie J., Dustin E. Sweet, Branimir Šegvić, Charles C. Monson, Giovanni Zanoni, Stephen Marshak, and Melanie A. Barnes. 2020. “Paleotopography Controls Weathering of Cambrian-Age Profiles beneath the Great Unconformity, St. Francois Mountains, SE Missouri, USA.” Journal of Sedimentary Research 90 (6): 629–50.

Roth, Ariel A. 2009. “‘Flat Gaps’ in Sedimentary Rock Layers  Challenge Long Geologic Ages.” Journal of Creation, August. https://creation.com/flat-gaps.

Sappenfield, Aaron Dale. 2015. “Precambrian-Cambrian Sedimentology, Stratigraphy, and Paleontology in the Great Basin (Western United States).” PhD Dissertation, UC Riverside. https://escholarship.org/uc/item/4r02d6xr.

Sharp, Robert P. 1940. “Ep-Archean and Ep-Algonkian Erosion Surfaces, Grand Canyon, Arizona.” GSA Bulletin 51 (8): 1235–69. https://doi.org/10.1130/GSAB-51-1235.

Snelling, Andrew A. 2021. “The Petrology of the Tapeats Sandstone, Tonto Group, Grand Canyon, Arizona.” Answers Research Journal 14. https://assets.answersingenesis.org/doc/articles/pdf-versions/arj/v14/petrology_tapeats_sandstone.pdf.

———. 2023. “The Carbon Canyon Fold, Eastern Grand Canyon, Arizona.” Answers Research Journal 16. https://answersresearchjournal.org/geology/carbon-canyon-fold-arizona/.