Palynologic evidence for the age of the Abiquiu Formation, north-central New Mexico

The Abiquiu Formation crops out on the north side of the Jemez Mountains and Nacimiento uplift in the western part of the Espanola basin of north-central New Mexico. This formation has been divided into three informal units: the upper member, the Pedernal member and the lower member. Vertebrate fossils from the upper member are early Miocene. Regional correlations based on lithology and stratigraphic position suggest that the lower two members of the Abiquiu are upper Oligocene to lower Miocene. South of the Nacimiento uplift, there are extensive outcrops of Zia Sand of early to middle Miocene age based on vertebrate fossils. Between the exposures of Abiquiu Formation and Zia Sand, there are scattered outcrops tentatively identified as Abiquiu. Four stratigraphic sections were selected and sampled for pollen to try to determine the age of the Abiquiu Formation and its stratigraphic relation to the Zia Sand. Samples were collected from the upper member of the Abiquiu Formation near the village of Abiquiu and the Pedernal member near Nacimiento Peak. The lower member was not recognized at the time of this study, and no samples were collected from it. The Zia Sand was sampled at its type locality, and beds resembling Abiquiu were sampled near the village of Gilman. The majority of samples were barren, but sufficient pollen was recovered to show that the suites at all four localities are similar. The most diagnostic taxa are the Compositae which indicate a maximum age of late Oligocene for all of the sampled strata. The pollen do not clearly establish the equivalence of the Abiquiu Formation and Zia Sand. Vertebrate fossils reported by other workers suggest that the upper member of the Abiquiu is a partial stratigraphic equivalent of the Zia Sand.