New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Triassic Redonda Formation, the uppermost part of the Chinle Group in east-central New Mexico, yields extensive vertebrate ichnofossil assemblages that were first discovered in the 1930s. As much as 92 m thick, the Redonda Formation in its outcrop belt along the northwestern edge of the Llano Estacado (Guadalupe and Quay counties, New Mexico) can be divided into five members (ascending order): Quay (a replacement name for Red Peak), San Jon Creek, Duke Ranch, Wallace Ranch and Montoya Point (laterally equivalent to the Duke Ranch and Wallace Ranch members). Redonda deposition took place in a palustrine system that comprised a mosaic of lakes, lake margins, fluvial channels, floodplains and stable interfluves. Most of the Redonda ichnofossil assemblages are from lake margin facies abundantly preserved in the San Jon Creek Member. Presumed lungfish burrows from the Redonda Formation pertain to Redondarefugium abercrombieorum and are vertical to obliquely oriented, slightly helical, unlined burrows with a round cross section, little ornamentation of the burrow walls and a flaskshaped terminus. Redonda Formation tetrapod footprints are assigned to: Brachychirotherium parvum, Brasilichnium elusivum, Characichnos ichnosp., Evazoum ichnosp., Grallator cursorius, Gwyneddichnium (= “Apachepus”) cottonorum and Rhynchosauroides ichnosp. Redonda tetrapod footprints represent the Brontopodus ichnofacies, more specifically the Evazoum ichnocoenosis. The track assemblages of the Chinle represent a global Late Triassic footprint record dominated by the tracks of crurotarsans, dinosaurs and sphenodonts.