For many decades, creation scientists have included the Sixtymile Formation in Grand Canyon as part of the Sauk Megasequence that marks the onset of the global Flood.¹ They based their conclusions on empirical data contained within the rock unit itself. And now, the secular geological community has arrived at a similar conclusion.²
 
Stopping short of admitting the possibility of a global Flood, Karl Karlstrom, from the University of New Mexico, and colleagues from the Denver Museum of Nature and Sciences, the University of Arizona, the University of Calgary, Boise State University, and Monash University (Australia) found that the Sixtymile Formation in eastern Grand Canyon is much younger than originally thought.²

Both creation and secular scientists agree that the Sixtymile Formation is part of the Sauk Megasequence.

The Sixtymile Formation is largely composed of sandstones and breccias (rock made up of fragments of angular rocks), and occasional mudstones, and is approximately 200 feet thick at its maximum. Until this study, it was thought to be part of the Late Precambrian or Neoproterozoic succession.²
 
Karlstrom and his research team dated the Sixtymile Formation and the overlying Tapeats Sandstone using detrital zircons found in the sandstones.³ They published their findings in Nature Geoscience, concluding that the Sixtymile Formation must have been deposited just prior to the deposition of the overlying Tapeats Sandstone, with no significant time gap.²
 
Lead author, Karlstrom stated,

At first glance it seemed to contradict fossil evidence, but, using new global constraints, we document that Tonto Group⁴ trilobites lived on Earth 505-500 million years ago such that the precise new geochronology and fossil evidence are in mutual agreement. Thus, flooding of the North American continent took place within a geologically short interval between 505 and 500 million years ago—more recently and much more rapidly than previously thought.^5,6

The authors went on to explain, “Cambrian strata globally record the transgressive inundation of many continents by advancing oceans that deposited sheet sands, muds and carbonates. This prolonged sedimentary onlap took place in pulses, each followed by sedimentary offlap, such that the Sauk ‘megasequence,’ is bounded by and includes important internal unconformities.”²
 
The Sauk Megasequence is merely the first of six megasequences ICR has been studying in our global Column Project.⁷ ICR views the Sauk as the first major advance—a “pulse” if you will—of the floodwaters onto the continents at the onset of the global Flood. We found that
   
In 1994, creation scientists Steve Austin and Kurt Wise formulated their interpretation that the Sixtymile Formation is the bottom unit of the Sauk Megasequence in Grand Canyon using observable sedimentological evidence within the strata, noting that the Sixtymile Formation contains large angular clasts indicative of high-energy deposition at the onset of the Flood.¹ Karlstrom and his co-authors arrived at the same result (that the Sauk includes the Sixtymile Formation) based on their age-dating of detrital zircons. However, they believe this unit marks the beginning of the first of several flooding events.²
 
Both creation and secular scientists agree that the Sixtymile Formation is part of the Sauk Megasequence. But because they have a different worldview, secular scientists continue to struggle to explain the Cambrian strata, the Sauk Megasequence, and the significance of the Sixtymile Formation, asking:
 

The Bible describes one global Flood, with several advances—or “pulses”—that laid down the geological layers we see today, an event that occurred just thousands of years ago.

Accepting the book of Genesis as accurate history provides solid answers to all of these questions. The Bible describes one global Flood, with several advances—or “pulses”—that laid down the geological layers we see today, an event that occurred just thousands of years ago. The Flood buried billions of organisms, starting with the Sauk Megasequence and the Sixtymile Formation in Grand Canyon. There is no mystery when we have the written Word of God.

References
1. Austin, S. A. and K. P. Wise. 1994. The pre-Flood/Flood Boundary: As Defined in Grand Canyon, Arizona and eastern Mojave Desert, California. In Proceedings of the Third International Conference on Creationism, R. E. Walsh (Ed.), 37–47.
2. Karlstrom, K. et al. 2018. Cambrian Sauk transgression in the Grand Canyon redefined by detrital zircons. Nature Geoscience. 11: 438-443.
3. This age-dating technique, although not absolute, seems to allow comparison of relative ages of sandstones.
4. The Tonto Group includes the Cambrian Tapeats Sandstone, Bright Angel Shale, and Muav Limestone that were deposited on top of the Sixtymile Formation.
5. Carr, S. 2018. Cambrian Sixtymile Formation of Grand Canyon yields new findings. Posted on Phys.Org on June 1, 2018, accessed June 15, 2018.
6. We are not advocating the millions of years claimed by secular science, but the rapid and recent flooding creation geologists have maintained all along.
7. Clarey, T. 2015. Grappling with Megasequences. Acts & Facts. 44 (4): 18-19.
8. Clarey, T. 2018. Minimal continental coverage during the early Flood. Acts & Facts. 47 (3): 8-9.

*Dr. Timothy Clarey is Research Associate is at ICR and earned a doctorate in geology from Western Michigan University.