New Mexico Geological Society Annual Spring Meeting — Abstracts

The vast majority of tetrapod tracks in the Upper Triassic Chinle Group of the western United States occur in the Rock Point sequence, which is of Apachean (late NorianI Rhaetian) age. These tracks are important for several reasons, including: (1) they represent the most diverse Late Triassic tetrapod track assemblages in western North America; (2) they provide evidence of faunas that are poorly represented by body fossils; and (3) they provide a basis for correlation with the tetrapod faunas of the Late Triassic of eastern North America, which are predominantly represented by ichnofaunas.

The Apachean Sloan Canyon Formation of northeastern New Mexico contains a number of significant tetrapod ichnofaunas, including Peacock Canyon and Sloan Canyon. A newly discovered tetrapod tracksite is present in the floor of Sloan Creek in Union County, New Mexico (sec. 15, T5N, R35E). The tracksite is in the middle part of the Sloan Canyon Formation and covers a minimum area of 2000 square meters. Sediments at the tracksite represent playa sandflat and playa margin deposits.

At Sloan Creek, tracks occur at eight distinct stratigraphic levels in a 1.5-meterthick interval of red and green mottled, fine-grained sandstone and siltstone. The most common tracks are identified as Pseudotetrasauropus (prosauropod dinosaur), and occur at five levels. Less common, each only occurring at a single level, are tracks assigned to Brachychirotherium (aetosaur?), Grallator (theropod dinosaur) and Tetrasauropus (sauropod dinosaur?). The Sloan Creek site differs from Sloan Canyon in lacking large tridactyl theropod tracks and from Peacock Canyon in lacking Rhynchosauroides, Kouphichnium and putative therapsid tracks.