LATE HEMINGFORDIAN-BARSTOVIAN MAMMALIAN BIOSTRATIGRAPHY OF THE MIDDLE MIOCENE TESUQUE FORMATION, ESPANOLA BASIN, NORTH-CENTRAL NEW MEXICO

The Barstovian North American Land Mammal Age (NALMA) of the middle Miocene Epoch is largely defined using the Barstow Formation within southern California. Therefore, an examination of the biostratigraphy of other regions is needed to test the validity of the established biostratigraphic framework. This study examines the biostratigraphy of the Tesuque Formation in the Española Basin of north-central New Mexico. The Tesuque Formation is well exposed within the northeastern region of the Española Basin and captures the Mid-Miocene Climatic Optimum (MMCO) and the progressive global cooling event thereafter. This basin comprises a nearly continuous record of sediment deposition that contains mammalian fauna from the late Hemingfordian to the Hemphillian NALMAs and over 40 volcanic ash beds, many of which have been radiometrically dated. The Española Basin, therefore, provides a unique opportunity to (1) aid in calibrating the middle Miocene mammalian biostratigraphy and (2) aid in assessing environmental-faunal interactions across the MMCO and transition period. Over this climatic transition, there was a shift in both flora and fauna. During the MMCO, palm fossils were present, indicating warmer conditions and bristlecone pine fossils were present during the later cooling period, indicating cooler conditions. There was also a noticeable transition of megafauna between the MMCO and the transition period. For example, camelids were more abundant during the MMCO, whereas antilocaprids became more abundant during the climate transition.