Jurassic stratigraphic nomenclature for northwestern New Mexico
— Steven M. Cather


Nomenclatural debates concerning Jurassic strata of northwestern New Mexico are long-standing and contentious. I present arguments here that support the following: (1) The term Wanakah Formation has little utility in New Mexico, where its two constituent members are typically mapped as formations. The lower of these two formations is the Todilto Formation. The upper should be termed the Beclabito Formation, as these strata cannot be confidently correlated to the type Summerville Formation of central Utah. (2) The Bluff Sandstone should be a broadly inclusive unit that encompasses all prominent eolianites above the Beclabito and its equivalents, and should be regarded as a formation within the eolianite-bearing San Rafael Group. (3) The Recapture Member should remain part of the Morrison Formation because, despite containing eolianites and sabkha deposits, much of the unit is fluvial. The contact between eolianites and fluvial strata within it is commonly not well enough exposed to be mapped reproducibly. (4) The Westwater Canyon Member of the Morrison Formation is a valid term and should not be renamed the Salt Wash Member. (5) The Jackpile Sandstone Member should be removed from the Morrison Formation and instead should be mapped as the Lower Cretaceous Jackpile Sandstone or as Burro Canyon Formation.

In general, lithologic identity (depositional environment) provides the best basis for nomenclature. Lateral correlation and stratigraphic subdivision using unconformities in the Jurassic section have proven problematic, because many such unconformities are not regional in scope and are likely diachronous.

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Recommended Citation:

  1. Cather, Steven M., 2021, Jurassic stratigraphic nomenclature for northwestern New Mexico, in: New Mexico Geological Society, 71st Annual Fall Field Conference, September 2021, Geology of Mount Taylor, Frey, Bonnie A.; Kelley, Shari A.; Zeigler, Kate E.; McLemore, Virginia T.; Goff, Fraser; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, pp. 251-258. https://doi.org/10.56577/FFC-71.251

[see guidebook]