Coal geology of the lower Moreno Hill Formation, Salt Lake Field, west-central New Mexico
Gretchen K. Hoffman
The Salt Lake coal field in west–central New Mexico is defined by the arcuate outcrops of the Moreno Hill Formation of Late Cretaceous, Turonian age. This formation is divided into three informal units, the lower, middle and upper members. The lower member contains the Antelope, Cerro Prieto and Rabbit informal coal zones, in ascending order. The Antelope zone, just above the underlying marine Atarque Sandstone, has two relatively thin, high sulfur (1.2% avg.) coals in a fine-grained sequence deposited in a back–barrier swamp environment. As many as five coal beds are in the medial Cerro Prieto zone, although only two of these coastal–plain coals have lateral continuity. These coals range from 1 to 14 ft thick and often contain persistent claystone (tonstein) partings. The low sulfur (0.7%) coastal–plain Cerro Prieto coals developed landward of the marine Fite Ranch Member (Tres Hermanos Formation) pinchout and represent the majority of the economic coal resource in the Salt Lake field. The Rabbit zone contains up to four coal beds of fluvial swamp origin. The second bed above the base attains economic thickness (7.5 ft). All of the Moreno Hill lower member coals are relatively high in ash (18%) and combustion analyses indicate an average apparent rank of subbituminous C, although vitrinite reflectance data show a slightly higher rank, high volatile bituminous C. These coals tend to have a higher percentage of inertinite macerals than other coals from northwestern New Mexico, probably a result of greater oxidation or charring of the swamps before burial.
- Hoffman, Gretchen K., 1994, Coal geology of the lower Moreno Hill Formation, Salt Lake Field, west-central New Mexico, in: Mogollon Slope, west-central New Mexico, Chamberlin, Richard M.; Kues, Barry S.; Cather, Steven M.; Barker, James B.; McIntosh, William C., New Mexico Geological Society, Guidebook, 45th Field Conference, pp. 283-289.