Circular 186—Vertebrate paleontology, stratigraphy, and biostratigraphy of Eocene Galisteo Formation, north-central New Mexico

By S. G. Lucas, 1982, 34 pp., 2 tables, 17 figs., 2 appendices.

Describes and identifies vertebrate fossils from Galisteo Formation in precise stratigraphic context, correlates major outcrops, determines age of Galisteo, and correlates it with other formations. The purposes of this study were to: (1) describe and identify the vertebrate fossils known from the Galisteo Formation, (2) place these vertebrates in their precise stratigraphic context in the Galisteo Formation, (3) use vertebrate fossils and rock-stratigraphy to correlate major outcrops of the Galisteo Formation with each other, and (4) determine the age of the Galesteo Formation and correlate it with other formations both in and outside of New Mexico. In accomplishing these purposes, the author hopes to provide a precise chronologic framework for the Galisteo Formation that will aid further in deciphering the early Tertiary history of north-central New Mexico.

The early Tertiary history of the Rio Grande rift in New Mexico presents a challenging problem to geologists. Prior to the initiation of the rifting, fluvial deposition took place in several sedimentary basins in central New Mexico. The resultant deposits of sandstone, siltstone, mudstone, and conglomerate were faulted and deformed by the rifting and, in some places, were buried under hundreds of meters of upper Tertiary sedimentary deposits and igneous rocks. The lower Tertiary sediments include the El Rito, Galisteo, and Baca Formations and are now generally exposed as isolated and structurally complex outcrops. Precise age and stratigraphic relationships are not fully understood.

Because these formations are mostly fluvial in origin, age relationships depend largely upon fossils of terrestrial plants and animals. Until recently few fossils have been reported from the Galisteo and Baca Formations, and no fossils have ever been reported from the El Rito Formation. However, the present study resulted in an extensive collection of vertebrate fossils from the Galisteo Formation in and around the northern Albuquerque Basin to determine more precisely the age, correlation, and stratigraphic relationships of these rocks.