Raton Formation

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The Raton Formation is a geological formation of Upper Cretaceous and Paleocene age which outcrops in the Raton Basin of northeast New Mexico and southeast Colorado.

The Raton Formation was originally named "Raton Hills Group" by Hayden in 1869 for coal beds in the Raton Hills in Colfax County, New Mexico. In 1913, Lee changed the name to Raton Formation. Lee described the formation [1] as a coal with carbonaceous shale with brown to buff sandstone and conglomerate (usually at the base). The Raton Formation is about 1140 feet thick at the type locality. The formation unconformably overlies the Vermejo Formation, and unconformably (?) underlies the Poison Canyon Formation.

In 1954, Brown [2] determined that the Raton Formation was of Late Cretaceous and Paleocene age.

Pillmore[3] measured the formation thickness as 2000 feet, and divided the Raton Formation into three divisions. The lowest division is a basal sandstone and conglomerate of quartzite, chert and gneiss pebbles and cobbles in a coarse-grained quartzose to arkosi sandstone matrix. The middle division is fine to coarse grained sandstone, with some siltstone, mudstone, and coal. The upper division is coal-bearing and contains sandstone, siltstone, mudstone, shale, and mineable coal.[4]

Because the Raton Formation is a well-preserved sequence of rocks spanning the Cretaceous-Paleogene boundary, it has been studied for evidence of a large meteor impact at the end of the Cretaceous that is thought to have caused the Cretaceous–Paleogene extinction event. The boundary is represented by a 1-cm thick tonstein clay layer which has been found to contain anomalously high concentrations of iridium. The boundary clay layer is accessible to the public at Trinidad Lake State Park, among other places in the Raton Basin.

References[edit]

  1. ^ Lee, 1913, US Geological Survey Professional Paper 101, p. 55-61.
  2. ^ Brown, 1954, Geological Society of America Bulletin, v. 54, p. 65-86.
  3. ^ Pillmore, 1969, Mountain Geologist, v. 6, p. 129.
  4. ^ M.E. Maclachlan, New Mexico Geological Society Guidebook, 27th Field Conference, Vermejo Park, 1976