The Upper Cretaceous (Turonian) Juana Lopez Beds of the D-Cross Tongue of the Mancos Shale in central New Mexico and their relationship to the Juana Lopez Member of the Mancos Shale in the San Juan Basin

Research reveals that the Juana Lopez Member of the Mancos Shale, previously recognized only in the San Juan Basin, extends into central New Mexico as the Juana Lopez Beds within the D-Cross Tongue. This extension is characterized by thinner calcarenites and sandstones interbedded with shales, suggesting significant condensation and potential erosional unconformities across its geographic extent. The study identifies a distinctive fossil assemblage, including the oyster Cameleolopha lugubris and ammonite Prionocyclus macombi, which provides biostratigraphic resolution but is not universally present in all outcrop sections. Chronostratigraphic analysis indicates that neither the upper nor lower contacts of the Juana Lopez represent regional isochronous surfaces, complicating correlations across New Mexico.

Hook, S. C., & Cobban, W. A. (2013). The Upper Cretaceous (Turonian) Juana Lopez Beds of the D-Cross Tongue of the Mancos Shale in central New Mexico and their relationship to the Juana Lopez Member of the Mancos Shale in the San Juan Basin. New Mexico Geology, 35(3), 59–81. https://doi.org/10.58799/nmg-v35n3.59