Stratigraphy, age and correlation of the Upper Cretaceous Tohatchi Formation, western New Mexico
Spencer G. Lucas, Dennis R. Braman, and Justin A. Spielmann
The Upper Cretaceous Tohatchi Formation is at least 160 m of nonmarine siliciclastic strata exposed in extreme western New Mexico along the southeastern and eastern fl ank of the Chuska Mountains. The Tohatchi Formation conformably overlies the Menefee Formation, is unconformably overlain by the Deza Member of the Chuska Formation and consists of two members named here, a lower, sandstonedominated Separate Hill Member and an upper, mudstone-dominated Red Willow Wash Member. A signifi cant change in sandstone lithology and bedform at the base of the Tohtachi Formation is a mappable contact and justifi es continued recognition of the unit as a distinct formation.
Dinosaur fossils found throughout the Tohatchi Formation indicate it is of Late Cretaceous age, and we report extensive palynomorph assemblages that refi ne this age assignment to early Campanian. The Tohatchi Formation is not, as has been thought for 50 years, a correlative of part of the upper Campanian Pictured Cliffs-Fruitland-Kirtland formations succession to the west. Instead, the Tohatchi Formation is the uppermost part of the Mesaverde Group in western New Mexico, younger than the underlying Allison Member of the Menfee Formation locally, and older than the late Campanian turnaround of the Cliff House-Pictured Cliffs shoreline to the east.
- Lucas, Spencer G.; Braman, Dennis R.; Spielmann, Justin A., 2003, Stratigraphy, age and correlation of the Upper Cretaceous Tohatchi Formation, western New Mexico, in: Geology of the Zuni Plateau, Lucas, Spencer G.; Semken, Steven C.; Berglof, William R.; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 54th Field Conference, pp. 359-368.