Frenchman Mountain Dolostone

Frenchman Mountain Dolostone
Stratigraphic range: Middle Cambrian
498–497 Ma
↓

[1]
TypeGeological formation
Unit ofTonto Group[1]
UnderliesTemple Butte Formation in Frenchmen Mountain to western Grand Canyon. Redwall Limestone and locally Temple Butte Formation in central Grand Canyon.
OverliesMuav Limestone
Thicknessup to 370 m (1,210 ft)
Lithology
Primarydolomite
Othershale
Location
RegionNorthern Arizona (Grand Canyon) and southern Nevada.
CountryUnited States of America
Type section
Named forFrenchman Mountain, Nevada
Named byV. S. Korolev[2] and K. E. Karlstrom, S. M. Rowland and others[1][3]
LocationFrenchman Mountain, Nevada
Year defined2023
Coordinates36°11′29″N 115°00′27″W / 36.1915°N 115.0076°W / 36.1915; -115.0076
Regionsouthern Nevada
CountryUnited States of America
Thickness at type section370 m (1,210 ft)

The Frenchman Mountain Dolostone is the uppermost and youngest of five Cambrian geologic formations that comprise the Tonto Group. It consists of beds of mottled white to gray dolomite often separated by thin seams of shale, especially in its lower part. In the Grand Canyon, this formation forms vertical cliffs that thicken westward between the top of the Muav Limestone and the base of either the Devonian Temple Butte Formation or Mississippian Redwall Limestone. Because of unidentified trace fossils and lack of datable body fossils, the Frenchman Mountain Dolostone exact age is uncertain. Within the Grand Canyon, its thickness varies between 61 and 137 m (200 and 449 ft). West into the Lake Mead region, it thickens abbr=on and is 370 m (1,210 ft) thick at Frenchman Mountain near Las Vegas, Nevada.[1][3][4]

  1. ^ a b c d Karlstrom, K.E., Mohr, M.T., Schmitz, M.D., Sundberg, F.A., Rowland, S.M., Blakey, R., Foster, J.R., Crossey, L.J., Dehler, C.M. and Hagadorn, J.W., 2020. Redefining the Tonto Group of Grand Canyon and recalibrating the Cambrian time scale. Geology, 48(5), pp. 425–430.
  2. ^ Korolev, V.S., 1997, Sequence stratigraphy, sedimentology, and correlation of the undifferentiated Cambrian dolomites of the Grand Canyon and Lake Mead area [M.S. thesis]. University of Nevada, Las Vegas, 178 p.
  3. ^ a b Rowland, S.M., Korolev, S., Hagadorn, J.W. and Ghosh, K., 2023. Frenchman Mountain Dolostone: A new formation of the Cambrian Tonto Group, Grand Canyon and Basin and Range, USA. Geosphere, 19(3), pp.719-747.
  4. ^ Middleton, L.T. and Elliott, D.K., 2003. Tonto Group, in Beus, S. S., and Morales, M., eds. Grand Canyon geology Museum of Northern Arizona Press, Flagstaff, Arizona. pp. 90–106.