New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Triassic (Rhaetian) Redonda Formation is widely exposed in east-central New Mexico, but vertebrate body-and ichnofossils are restricted to Quay county. The Redonda in this area represents a lacustrine margin sequence. Four taphofacies can be recognized: (1) nearshore, lacustrine taphofacies -tabular sandstones and mudstones formed near the lacustrine margin preserve complete and disarticulated fish; (2) carbonate lacustrine margin taphofacies-vertebrate tracks are preserved on the undersides of ledge-forming calcarenites which formed on lacustrine shorelines; the ichnofauna includes Brachychirotherium, Grallator, Psudotetrasauropus, Tetrasauropus and Rhynchosauroides, the latter two of which are reported for the first time; (3) beach conglomerate taphofacies-conglomerates formed in high energy shallow water or on beaches are predominantly composed of fish scales and other ichthyoliths, but also contain abundant phytosaur teeth and rarer rauisuchian and aetosaur material; (4) fluvial channels taphofacies intraformational conglomerates and lenticular sandstones, representing fluvial channel deposits, contain fragmentary and abraded bones; locally, small channels are full of wellI preserved bones which are dominantly phytosaurian, but also include ?poposaur and aetosaur specimens: (5) floodplain taphofacies -isolated phytosaur postcrania and skulls are found in mudrocks formed in proximal floodplain environments; and (6) paleosol taphofacies -accumulations of small tetrapods occur in mottled mudrocks containing calcareous concretions which represent paleosols. The Redonda Formation contains a greater range of vertebrate taphofacies than other formations in the Chinle Group of the western United States because of its extensive lacustrine, as well as fluvial, facies.