Lower Cretaceous ammonites from southwestern New Mexico
— Spencer G. Lucas
Lower Cretaceous ammonites are present in Aptian–Albian strata of the U-Bar and Mojado formations of the Bisbee Group in the central Peloncillo Mountains, Animas Mountains, Little Hatchet Mountains, Big Hatchet Mountains and the Cookes Range of southwestern New Mexico. The oldest ammonites are from the Carbonate Hill Member of the U-Bar Formation and include the taxa Hypacanshoplites immunitus (Stoyanow), Kazanskyella spathi (Stoyanow), K. fosteri (Scott), K. arizonica Stoyanow, Stoliczkaia patagonica (Stoyanow), and Parahoplites sp. These are ammonites of the Kazanskyella spathi Zone of latest Aptian age. Ammonites a UM the overlying Old Hachita Member of the U-Bar Formation are Beudanticeras newtoni Casey,
Douvilleiceras sp. aff. D. mammillatum (Schlotheim), and Hypacanthoplites sp. These are ammonites of the early Albian Douvilleiceras sp. cf. D. mammillatum Zone. The Fryingpan Spring Member of the Mojado Formation yields anunonites of the late Albian Mortoniceras equidistans Zone, including Mortoniceras equidistans (Cragin), M. cf. M. leonense (Conrad) and Eopachydiscus marcianus (Shumard). The youngest Lower Cretaceous ammonoids from southwestern New Mexico are specimens of Engonoceras serpentinum (Cragin) from the upper Mojado Formation indicative of the latest Albian Drakeoceras drakei Zone. Lower Cretaceous ammonites thus represent four ammonite zones that well-constrain correlation of portions of the Bisbee Group in southwestern New Mexico.
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- Lucas, Spencer G., 2000, Lower Cretaceous ammonites from southwestern New Mexico, in: Southwest passage. A trip through the Phanerozoic, Lawton, Timothy F.; McMillan, Nancy J.; McLemore, Virginia T., New Mexico Geological Society, Guidebook, 51st Field Conference, pp. 195-201. https://doi.org/10.56577/FFC-51.195