TOWARD STANDARDIZATION OF PHANEROZOIC STRATIGRAPHIC NOMENCLATURE IN NEW MEXICO

Recent decades have seen an unprecedented rate of change in the Phanerozoic stratigraphic nomenclature of New Mexico. At the same time, the state has experienced a dramatic resurgence of geologic quadrangle mapping, primarily facilitated by the National Geologic Mapping Act of 1992, which enabled the STATEMAP and EDMAP programs. The utility of the new stratigraphic nomenclature has not yet been adequately tested, and in some cases has been opposed by other researchers. Despite a lack of consensus among stratigraphers, it is desirable to have an agreed-upon nomenclature for the purpose of ongoing geologic mapping. We present here, from our perspective as geologic mappers, revisions to the Phanerozoic stratigraphic nomenclature of New Mexico. We hope our discussion will eventually lead to adoption of a standardized nomenclature, for the purposes of mapping, by the New Mexico Bureau of Geology and Mineral Resources, which administers the STATEMAP and EDMAP programs in New Mexico.

Here we criticize, and suggest alternatives to, aspects of recent nomenclatural changes by S.G. Lucas and colleagues for Pennsylvanian, Permian, Triassic, Jurassic, and Paleogene strata. Specifically, we disagree with: (1) the application of the terms Gray Mesa Formation and Atrasado Formation to Pennsylvanian strata of southern New Mexico; (2) raising of the Lower Permian Yeso Formation to group rank; (3) replacement of the term Meseta Blanca Member with Arroyo de Alamillo Formation in the Yeso; (4) raising the Los Vallos and San Ysidro members of the Yeso to formation rank; (5) the mapping utility of some formation-rank units of the Upper Triassic Chinle Group; (6) the replacement of the term Dockum by Chinle in eastern New Mexico; (7) replacement of the term Westwater Canyon Member of the Jurassic Morrison Formation with Salt Wash Member; and (8) the replacement of the term Baca Formation by the Hart Mine Formation for middle Eocene strata in eastern Socorro County.