New Mexico Geological Society Annual Spring Meeting — Abstracts

In the Chama basin of north-central New Mexico, the Upper Triassic Salitral Formation, originally referred to as the Salitral Shale Tongue, is part of the lower Chinle Group, and is generally described as a blocky bentonitic mudstone with some interbedded sandstones and siltstones. The mudstones are mottled and contains carbonate nodules, indicating paleosol development. The Salitral Formation lies conformably above the Agua Zarca (=Shinarump) Formation and disconformably below the Pol eo Formation. Fossils recovered from the Salitral Formation indicate an Adamanian (late Carnian) age. The Salitral may be broken into three discrete lithostratigraphic units: a lower green mudstone, a thin media] sandstone bench, and an upper red mudstone. We propose formal designation of these units as members of the Salitral Formation.

The majority of the vertebrate fossils recovered from the Salitral Formation during survey work in the summer of 2002 were recovered from the bases of slopes in the upper member. The fossils are predominantly fragments of metoposaur amphibian skull and girdle elements, together with a few bone fragments that could only be referred to Archosauria indet. The bone fragments are abraded and moderately weathered, and are found mixed with calcrete nodules that cover the mudstone slopes. The calcrete nodules, as well as the vertebrate fossil material, are weathering out of the base of a very thick calcrete-pebble conglomerate at the base of the overlying Poleo Formation. However, while the fossils are weathering out of the basal Poleo Formation, they were most likely incorporated into the conglomerate as reworked Salitral clasts and thus were originally deposited in the upper Salitral Formation. The advanced degree of weathering indicates a moderate time of subaerial exposure (>3 years), while the abrasion of the surfaces indicates exposure and transport of the bone fragments.