The Coconino Sandstone, a well-known rock layer of the Grand Canyon and surrounding regions, has long been considered to be an example of an ancient eolian, or wind-blown, sandstone. However, literature review and prior research (in lab and field) have shown that it should be interpreted as a marine sandstone instead. Surrounding formations such as the Lyons, Tensleep, and Glorietta Sandstones show remarkably similar features to that of the Coconino–and geologist Dr. John Whitmore attempts to correlate them as being deposited during approximately the same geologic time period, analogous to a large “blanket” over much of the western U.S. states.
This study is significant in our understanding of Flood geology, as the similarities across these widespread Permian sandstones imply that they were likely deposited in a marine environment like the Coconino.
Whitmore’s research concludes that the Coconino sandstone can be correlated as a diachronous sand body that ranges all the way from North Dakota to southern California with a total area of approximately 2.4 million km2. Interestingly, provenance studies of the Coconino and its equivalents show that the origin of the sand likely came from across the entire continent–from eastern North America! This demonstrates that a massive amount of sand was eroded and transported across the country and deposited as a “blanket” over a large portion of the west. Paleocurrent data also supports this; consistent currents over such a big area favor a marine deposition model.
Additionally, other data collected from these sandstones strongly indicate subaqueous deposition. Cross-beds found in Coconino and its equivalents average an angle of about 20°, while in modern deserts the average is a much steeper 34°. The gentle slopes indicate that these sand waves formed underwater. Interestingly, other data at the microscopic level also point to marine deposition. In a modern sand dune, sand grains are typically well sorted and well rounded due to wind, and only more resistant minerals such as quartz remain. In the Coconino, though, the grains are poorly sorted (having various sizes) and sub-rounded to sub-angular. And even soft minerals such as micas have been found! Micas like muscovite and biotite rarely last in wind-blown settings, and so it is significant that they have been found in the Coconino and other Permian sandstones.
These findings, along with other collected data and studies, have led Whitmore and others to conclude that these sandstones are not only correlated as one diachronous body, but that they have been deposited in a marine environment. This is consistent within a Flood model; the Coconino was likely laid down as Flood waters surged over the supercontinent of Pangea.
- Whitmore, John H. 2019. “Lithostratigraphic Correlation of the Coconino Sandstone and a Global Survey of Permian “Eolian” Sandstones: Implications for Flood Geology.”
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