THE STRATIGRAPHIC POSITION OF FOSSIL VERTEBRATES FROM THE POJOAQUE MEMBER OF THE TESUQUE FORMATION (MIDDLE MIOCENE, LATE BARSTOVIAN) NEAR ESPAÑOLA, NEW MEXICO

The stratigraphy of the Pojoaque Member of the Tesuque Formation near Española, NM is not well understood. This region, during the Middle Miocene, represented a dynamic alluvial fan-fluvial-lacustrine environment within the Española Basin while the Rio Grande Rift was active. Cavazza (1986) identified two paleodrainage systems (lithosome A, basin-margin facies and B, basin-floor facies) by means of sandstone and conglomerate petrology, paleocurrent, and sedimentary facies analyses. After x-ray diffraction analyses of claystones within lithosome B, mordenite was discovered, which is a zeolite mineral commonly found within volcanic rocks. This is significant because the presence of mordenite confirms Cavazza’s (1986) conclusion that lithosome B was sourced by the Taos Plateau–Latir volcanic fields. The objective of this study was to identify the stratigraphic position of vertebrate fauna of the Pojoaque Member of the Tesuque Formation using known fossil locality data, newly discovered fossil locality data, and measured sections of the Pojoaque Member. A faunal list was compiled that incorporates all vertebrates that have been taxonomically described from the Pojoaque Member, as well as first appearance datum. Two new vertebrate species were also described. Fossils discovered within the Pojoaque Member are almost exclusively found within relatively thin (0.5–3 m) maroon-red and pale green claystone to fine-grained siltstone beds of lithosome B which were concluded to likely be small lacustrine deposits. Unfortunately, it was not common practice for early paleontologists to record specific geographic locations of fossils. Therefore, this study was restricted to relatively recently published paleontological data, fossils discovered during this study, and coarse stratigraphic ranges of common fossil collecting localities to identify the stratigraphic positions of the fossil specimens. Many previous explorations recorded fossils singly from the Santa Cruz Red bed; in reality, there are multiple red horizons. Seven stratigraphic transects were measured across eight sections in the Española Basin. Examinations of the stratigraphic distribution of these fossiliferous beds have led to the conclusion that the Santa Cruz localities span the entire member. It was also concluded that making lithostratigraphic correlations within the Pojoaque Member across the Española Basin would be difficult, if not impossible, on account of the variability of the lithology