MSGID: 1:317/3 645334e6   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Frenchman mountain dolostone: 500 million-year-old grand canyon rock   
   layer finally gets a name    
    Geologists name ancient rock layer after Las Vegas mountain that contains   
   similar strata    
      
     Date:   
         May 3, 2023   
     Source:   
         University of Nevada, Las Vegas   
     Summary:   
         A research team outlines how it identified and bestowed a moniker   
         upon a previously unexplored 500 million-year-old Grand Canyon   
         formation: The Frenchman Mountain Dolostone. The newly named rock   
         layer has lain hidden in plain sight throughout the Grand Canyon   
         for millennia, but -- until now -- geologists had not named it or   
         studied it in detail.   
      
      
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   FULL STORY   
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   The Grand Canyon is one of the Seven Wonders of the World, visited by   
   millions of admirers each year. So, naturally, you'd think that all of   
   its rock layers had been studied and named. But you'd be wrong.   
      
   In a new report published this spring in the Geological Society of America   
   journal Geosphere, a UNLV-led research team outlines how it identified   
   and bestowed a moniker upon a previously unexplored 500 million-year-old   
   Grand Canyon formation: The Frenchman Mountain Dolostone.   
      
   The newly named rock layer has lain hidden in plain sight throughout   
   the Grand Canyon for millennia, but -- until now -- geologists had not   
   named it or studied it in detail.   
      
   The UNLV research team named it the Frenchman Mountain Dolostone (FMD)   
   -- after a similarly named mountain that lies adjacent to Las Vegas,   
   Nevada. That's where the FMD is thickest, most complete, and most   
   accessible for study.   
      
   Through scientific detective work, the researchers were able to narrow   
   down the age of this stratigraphic interval and its relationship to   
   strata in the Grand Canyon.   
      
   "For decades, geologists were unable to precisely correlate the succession   
   of strata at Frenchman Mountain with those in the Grand Canyon, in part   
   because Frenchman Mountain was tectonically displaced about 40 miles to   
   the west since the rocks were deposited," said lead author Steve Rowland,   
   an emeritus professor of geology at UNLV and paleontologist at the Las   
   Vegas Natural History Museum. "Establishing detailed descriptions and   
   thickness measurements of the strata at Frenchman Mountain and also   
   in the Grand Canyon has finally allowed us to solve this problem."   
   The FMD is over 1,200 feet thick at Frenchman Mountain, Rowland said,   
   but it thins dramatically toward the east. The portions exposed within   
   the Grand Canyon range in thickness from nearly 400 feet near the "West   
   Rim" Skywalk to less than 100 feet in Marble Canyon, in the eastern part   
   of Grand Canyon National Park.   
      
   In 1945, geologist Edwin McKee distinguished -- but did not formally   
   name - - the cliff-forming interval of rocks that occur just above the   
   well-known Muav Formation. The FMD contains no fossils, so McKee was   
   unsure of its age.   
      
   Rowland's team used a relatively new technique to determine the   
   FMD's age - - subtle differences in the ratio of stable isotopes of   
   carbon. Fluctuations in the ratios of these isotopes occurred at the same   
   time all over the Earth as the layers were deposited. The researchers   
   compared fluctuations in the Frenchman Mountain strata with those   
   identified in precisely dated rock layers elsewhere in the world. The   
   results indicate that the newly named formation was deposited over an   
   interval of 7.3 million years, during the Cambrian Period, between 502.8   
   million and 495.5 million years ago.   
      
   The FMD is the first new formation to be named in the canyon since 1985   
   when the Surprise Canyon Formation was named. It is also the first rock   
   layer exposed in the Grand Canyon to be named for a location outside   
   the Grand Canyon region.   
      
   In addition to Rowland, the research team included former UNLV graduate   
   student Slava Korolev, Denver Museum of Nature and Science geologist   
   James Hagadorn, and UNLV mathematics professor Kaushik Ghosh.   
      
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   Story Source: Materials provided by University_of_Nevada,_Las_Vegas. Note:   
   Content may be edited for style and length.   
      
      
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   Related Multimedia:   
       * Rock_layers_including_Frenchman_Mountain_Dolostone   
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   Journal Reference:   
      1. Stephen M. Rowland, Slava Korolev, James W. Hagadorn, Kaushik Ghosh.   
      
         Frenchman Mountain Dolostone: A new formation of the Cambrian   
         Tonto Group, Grand Canyon and Basin and Range, USA. Geosphere,   
         2023; DOI: 10.1130/GES02514.1   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230503200451.htm   
      
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