New Mexico Geological Society Annual Spring Meeting & Ft. Stanton Cave Conference — Abstracts

Upper Cretaceous strata exposed in the Chama Basin in Rio Arriba County in northern New Mexico contain ammonites and other marine molluscan fossils that span middle Cenomanian to middle Campanian time. Very few studies have been done on the Upper Cretaceous molluscan fossils in the Chama Basin. Landis and Dane (1967) published a geologic map of the Tierra Amarilla quadrangle with descriptions of geologic units and their fossil content. Muehlberger (1967) published the geology of the Chama quadrangle and also listed fossils from each geologic unit. Doney (1968) published the geology of the Cebolla quadrangle, also describing geology and listing fossils. Landis et al. (1974) published on the Cretaceous rocks and fossils of the Tierra Amarilla coal field. Lucas et al. (2009) documented a small assemblage of invertebrate fossils in the Dakota Sandstone near Ghost Ranch.

The Acanthoceras amphibolum Zone in the Paguate Sandstone Tongue of the Dakota Sandstone establishes a middle Cenomanian age for that unit. The Sciponoceras gracile biozone is present in the Graneros Shale, thus establishing a late Cenomanian age for that unit. In the Greenhorn Limestone, Watinoceras coloradoense indicates the lower Turonian Vascoceras birchbyi Zone, and the Mytiloides mytiloides inoceramid zone indicates the ammonite zone of Mammites nodosoides and thus a latest early Turonian age. The Collignoniceras woollgari Zone is present in the lower Carlile Member, establishing an earliest middle Turonian age for that unit, and the middle Turonian Prionocyclus hyatti Zone occurs higher in the Carlile. The ammonite zones present in the Juana Lopez Member are the earliest late Turonian Prionocyclus macombi Zone, the early late Turonian Scaphites warreni and S. ferronensis zones and the middle late Turonian S. whitfieldi Zone. The middle lower Coniacian Cremnoceramus crassus inconstans inoceramid zone is present in the Cooper Arroyo Sandstone Member and is equivalent to the Scaphites preventricosus ammonite zone. Santonian age invertebrates have not been collected from the study area. The Scaphites hippocrepis I Zone in the Satan Tongue establishes an early Campanian age for part of this unit. The lower middle Campanian zone of Baculites mclearni is present in the Lewis Shale.

References:

1. Doney, H. H., 1968, Geology of the Cebolla quadrangle, Rio Arriba County, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 92, 114 p.
2. Landis, E. R., Dane, C. H., and Cobban, W. A., 1974, Cretaceous rocks of the Tierra Amarilla Coal Field and adjacent areas, Rio Arriba County, New Mexico: New Mexico Geological Society, Guidebook 25, p. 231-238.
3. Landis, E. R., and Dane, C. H., 1967, Geologic map of Tierra Amarilla quadrangle, Rio Arriba County, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Geologic Map 19, scale 1:62,500.
4. Lucas, S. G., Rinehart, L. F. and Kelley, S., 2009, Cenomanian invertebrate assemblage from the Dakota Sandstone near Ghost Ranch, Rio Arriba County, New Mexico: New Mexico Geology, v. 31, p. 59-64.
5. Muehlberger, W. R., 1967, Geology of Chama quadrangle, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 89, 114 p.