Frenchman Mountain Dolostone | |
---|---|
Stratigraphic range: Middle Cambrian [1] | |
Type | Geological formation |
Unit of | Tonto Group[1] |
Underlies | Temple Butte Formation in Frenchmen Mountain to western Grand Canyon. Redwall Limestone and locally Temple Butte Formation in central Grand Canyon. |
Overlies | Muav Limestone |
Thickness | up to 370 m (1,210 ft) |
Lithology | |
Primary | dolomite |
Other | shale |
Location | |
Region | Northern Arizona (Grand Canyon) and southern Nevada. |
Country | United States of America |
Type section | |
Named for | Frenchman Mountain, Nevada |
Named by | V. S. Korolev[2] and K. E. Karlstrom, S. M. Rowland and others[1][3] |
Location | Frenchman Mountain, Nevada |
Year defined | 2023 |
Coordinates | 36°11′29″N 115°00′27″W / 36.1915°N 115.0076°W |
Region | southern Nevada |
Country | United States of America |
Thickness at type section | 370 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]