Refinements to the stratigraphic nomenclature of the Santa Fe Group, northwestern Albuquerque Basin, New Mexico

Recent geologic mapping refines the stratigraphic nomenclature of the Santa Fe Group in the Albuquerque Basin of the Rio Grande rift of central New Mexico. Discovery of an unconformity requires modifications to the stratigraphic nomenclature of the Santa Fe Group in the western Albuquerque Basin. The Rincones paleosurface represents a tectonostratigraphic boundary that separates slightly tilted, upper Miocene sediments of the Arroyo Ojito Formation from overlying, weakly consolidated, and subhorizontally stratified deposits of the Pliocene Ceja Formation. Correlation of the Rincones paleosurface constrains the distribution of component depositional belts across much of the basin and resolves a long-standing problem with stratigraphic correlations within the Albuquerque Basin. Revisions to the Santa Fe Group stratigraphic nomenclature in the northwestern Albuquerque Basin are intended to aid in future geologic mapping activities and in the interpretation of geologic compilations of the Albuquerque Basin. Use of the term “middle red formation” (or member) should be discontinued because it is ambiguously defined. The following revisions are proposed: raise the Cerro Conejo Member of the Zia Formation to formation rank; propose the Picuda Peak Member for the upper part of the Arroyo Ojito Formation; elevate the Ceja Member of the Arroyo Ojito Formation to formation rank and locally divide it into the Atrisco, Santa Ana Mesa, and Rio Puerco Members. The Pantadeleon Formation has similar composition to, and occupies the same stratigraphic position as, the Ceja Formation and should be abandoned as redundant to the senior term Ceja Formation.