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.

This research demonstrates how using fossil location data can permit one to infer their stratigraphic position from detailed geologic maps with stratigraphic studies. 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 along with fossils discovered during this study to identify the stratigraphic positions of the fossil specimens. It has been well documented and confirmed by recent field work that fossils of the Pojoaque Member have almost exclusively been produced from Lithosome B deposits; more specifically, relatively thin (.5–3m) pale-green and maroon-red claystone to fine-grained siltstone beds. Many previous explorations recorded fossils singly from the Santa Cruz Red bed; in reality, there are multiple red horizons. These fossil-bearing beds reflect either different depositional environments or a difference in diagenetic conditions. Nine stratigraphic transects were measured across eleven sections in the Española Basin. Examining the stratigraphic distribution of these beds within correlated Lithosome B outcrops using stratigraphic sections measured during field studies helped better define the stratigraphic positions of vertebrate fossils of the Pojoaque Member.