Miocene-Oligocene volcaniclastic deposits in the northern Abiquiu embayment and southern Tusas Mountains, New Mexico
— Daniel J. Koning, Kirt Kempter, Lisa Peters, William C McIintosh, and S. Judson May

Volcaniclastic sediment of the Santa Fe Group comprises a major portion of the basin-fill of the Abiquiu embay­ment, and these strata extend northward into the Tusas Mountains. The Abiquiu embayment lies between the Embudo fault system and the Colorado Plateau, and is generally considered as a northwest extension of the Española Basin. This volcanicla­stic sediment includes two general stratigraphic levels. The lower contains felsic-clast-dominated volcaniclastic conglomerate of the Cordito Member of the Los Pinos Formation, which interfingers to the southwest with white, tuffaceous sandstones of the Abiquiu Formation. At the top of the lower unit, conglomerate of the Cordito Member prograded southwestward over Abiquiu Formation sandstone. The upper volcaniclastic interval is composed of the Tesuque Formation. We propose applying the name Duranes Member (new name) to a purplish gray conglomerate, composed primarily of porphyritic dacite-andesite clasts, shed from volcanic sources in the southwestern Latir volcanic field (previously called the Plaza volcanic center). This conglomer­ate interfingers southwestward with orange, quartz-rich sandstone of the Chama-El Rito Member. A 50-100 m-thick tongue of fine- to medium-grained Chama-El Rito sandstone overlies the Duranes Member. New isotopic ages indicate that the contact between the lower and upper volcaniclastic intervals is diachronous: to the northeast it is ~23.5 Ma and to the southwest it is 20-21 Ma. A ⁴⁰Ar/³⁹Ar age on a basalt flow underlying the Abiquiu Formation indicates a maximum age of 25.5-26.0 Ma for this formation in the El Rito area. The top of the Duranes Member (Tesuque Formation) is 13.5-14.0 Ma and the top of the Chama-El Rito Member is ~13.5 Ma.