Revisions to the stratigraphic nomenclature of the Santa Fe Group, northwestern Albuquerque Basin, New Mexico
— Sean D. Connell, Daniel J. Koning, and Steven M. Cather

Geologic mapping and stratigraphic studies on the Cerro Conejo 7.5-minute quadrangle allow for finer subdivision of Santa Fe Group strata in the Albuquerque basin. We define four new stratigraphic terms (two formation-rank, two member-rank) to subdivide Santa Fe Group deposits in the northwestern margin of the Albuquerque basin and southwestern margin of the Santo Domingo basin. The term Cerro Conejo Member of the Zia Formation is assigned to deposits previously called the unnamed (upper) member of the Zia Formation or the middle red member of the Santa Fe Formation (now Santa Fe Group). At Arroyo Ojito, the Cerro Conejo Member is a 316-m-thick sequence of fine- to coarse-grained tabular to cross-bedded sandstone that is interpreted to have been deposited in sandy fluvial and eolian environments. The overlying Arroyo Ojito Formation is assigned to deposits previously called upper buff member of the Santa Fe Formation or Sierra Ladrones Formation (upper Santa Fe Group). At the type section, the Arroyo Ojito Formation is 437 m thick and is subdivided into, in ascending stratigraphic order, the Navajo Draw, Loma Barbon, and Ceja members. The uppermost unit exposed in Arroyo Ojito is named the Pantadeleon Formation, which represents deposition in faultcontrolled wedges produced by local accommodation along the hanging walls of major intrabasinal normal faults. The Cerro Conejo Member is interpreted to represent a transitional stratigraphic succession between eolian-dominated lower members of the Zia Formation and fluvially dominated strata of the overlying Arroyo Ojito Formation. Clasts of the Arroyo Ojito Formation contain variable proportions of red granite, volcanic rocks, chert, sandstone and Pedernal chert, indicating derivation from the eastern margin of the Colorado Plateau and Sierra Nacimiento. The Arroyo Ojito Formation was deposited by southeast-flowing progenitors to the Rio Puerco and Rio Jemez fluvial systems. Biostratigraphic, radioisotopic, and tephrochronologic data indicate that the Cerro Conejo Member was deposited during the middle Miocene. Much of the Arroyo Ojito Formation was deposited during the late Miocene and Pliocene; deposition ceased by the earliest Pleistocene. The Arroyo Ojito Formation interfingers with ancestral Rio Grande fluvial facies of the Sierra Ladrones Formation to the east. Correlatives of the Arroyo Ojito Formation include the Cochiti, Sierra Ladrones, and upper part of the Popotosa formations. The composite thickness of Santa Fe Group deposits exposed in the Cerro Conejo quadrangle is about 1060 m, approximately 20% of the maximum known basin-fill thickness at the basin depocenter.