Triassic stratigraphy of west-central New Mexico
Spencer G. Lucas and Steven N. Hayden
Triassic strata in west-central New Mexico are exposed over four, disjunct terranes: Largo Creek (western Catron County), Zuni Pueblo (western Cibola and southwestern McKinley counties), Bluewater (McKinley- Cibola counties) and Mesa Lucero (eastern Cibola–northern Socorro counties). The oldest Triassic strata in these terranes pertain to the Moenkopi Formation, which disconformably overlies the Permian San Andres Formation and is disconformably overlain by the Chinle Formation. The Moenkopi Formation in west-central New Mexico is as much as 68 m dominated by grayish-red and reddish-brown, lithic wackestones, mudstones and siltstones that yield charophytes, ostracodes, bones of capitosauroid amphibians and large footprints of Chirotherium reptiles indicative of an Early or Middle Triassic age.
Remaining Triassic strata in west-central New Mexico are assigned to five members of the Chinle Formation (in ascending order): Shinarump Member/mottled strata, Bluewater Creek Member, Petrified Forest Member (including lower and upper parts plus the Sonsela and Correo Sandstone beds), Owl Rock Member and Rock Point Member. As much as 24 m of silica-pebble conglomerate/sandstone and pedogenically modified and mottled siltstone, mudstone and sandstone pertain to the Shinarump Member and mottled strata. Root casts, previously identified as lungfish burrows, abound in the mottled strata near Fort Wingate.
The new term Bluewater Creek Member of the Chinle Formation is introduced here for strata in west-central New Mexico formerly termed Division D, lower red member or Monitor Butte Member of the Chinle Formation. The 100 m or more of Bluewater Creek Member are dominated by red sandstones and mudstones that contain an extensive fossil flora and some fossil vertebrates of Camian age. In west-central New Mexico, the overlying Petrified Forest Member is more than 1000 m divided into lower and upper, mudrock-dominated portions by the Sonsela Sandstone Bed, and contains the Correo Sandstone Bed near its top.
The youngest Triassic strata in west-central New Mexico pertain to the Owl Rock Member (as much as 24 m, exposed as far east as Thoreau) and Rock Point Member (50+ m) of the Chinle Formation. Putative Triassic strata near Horse Mountain, Catron County are Permian. and a supposed karst filling ("cave") in the San Andres Formation at Cottonwood Creek, McKinley County is a delta-plain facies of the Permian San Andres Formation.
- Lucas, Spencer G.; Hayden, Steven N., 1989, Triassic stratigraphy of west-central New Mexico, in: Southeastern Colorado Plateau, Anderson, Orin J.; Lucas, Spencer G.; Love, David W.; Cather, Steven M., New Mexico Geological Society, Guidebook, 40th Field Conference, pp. 191-211.