Raton Formation

The formation consists of coal with carbonaceous shale, brown to buff sandstone, and conglomerate (usually at the base). It is about 1,140 feet (350 m) thick at the type locality. The formation unconformably overlies the Vermejo Formation, and unconformably (?) underlies the Poison Canyon Formation.[1] It is of late Cretaceous to Paleocene age.[2]

The formation can be divided into three informal members.[3] The lowest member is a basal sandstone and conglomerate of quartzite, chert and gneiss pebbles and cobbles in a coarse-grained quartzose to arkosic sandstone matrix. The middle member is fine to coarse grained sandstone, with some siltstone, mudstone, and coal. The upper member 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.[5] The boundary clay layer is accessible to the public at Trinidad Lake State Park, among other places in the Raton Basin.

The Raton Formation was originally named "Raton Hills Group" by Ferdinand Vandeveer Hayden in 1869 for coal beds in the Raton Hills in Colfax County, New Mexico. In 1913, W.T. Lee changed the name to Raton Formation.[1]