Despite being a popular tourist destination that attracts millions of visitors every year, not all of the Grand Canyon’s rock layers have been thoroughly examined or given official names. However, a recent study published in the journal Geosphere, led by researchers from the University of Nevada, Las Vegas, has identified and named a previously unexplored formation within the canyon. Known as the Frenchman Mountain Dolostone, this 500 million-year-old rock layer has been hiding in plain sight for centuries, but has finally received the attention and recognition it deserves.
The newly discovered Grand Canyon formation was given the name Frenchman Mountain Dolostone (FMD) by the UNLV research team. This name was inspired by the nearby Frenchman Mountain located near Las Vegas, Nevada, where the FMD is most extensive and easily accessible for study. By conducting scientific investigations, the researchers were able to determine the age of this layer of rock and how it relates to other strata in the Grand Canyon.
Previously, geologists faced difficulties in correlating the succession of strata at Frenchman Mountain with those in the Grand Canyon due to tectonic displacement that occurred around 40 miles to the west during the rock’s deposition. However, detailed descriptions and measurements of the strata at both Frenchman Mountain and the Grand Canyon allowed the researchers to solve this problem, as explained by Steve Rowland, the lead author of the study and a paleontologist at the Las Vegas Natural History Museum.
According to lead author Steve Rowland, the Frenchman Mountain Dolostone (FMD) is more than 1,200 feet thick at Frenchman Mountain but thins considerably towards the east. Within the Grand Canyon, the thickness of the FMD varies, ranging from nearly 400 feet near the “West Rim” Skywalk to less than 100 feet in Marble Canyon, located in the eastern section of the national park.
In 1945, geologist Edwin McKee identified a cliff-forming interval of rocks above the well-known Muav Formation, but the interval was not officially named at the time as it lacked fossils, and its age was uncertain. Rowland’s team used a modern technique that involved examining the ratio of stable isotopes of carbon to determine the FMD’s age. By comparing fluctuations in the Frenchman Mountain strata with those in precisely dated rock layers worldwide, the researchers found that the FMD was deposited during the Cambrian Period over an interval of 7.3 million years, between 502.8 million and 495.5 million years ago.
The FMD is the first new formation to be named in the Grand Canyon since the Surprise Canyon Formation in 1985, and it is also the first to be named after a location outside of the canyon area. Rowland’s team included former UNLV graduate student Slava Korolev, Denver Museum of Nature and Science geologist James Hagadorn, and UNLV mathematics professor Kaushik Ghosh.
Source: University of Nevada, Las Vegas