TRACE FOSSIL ASSEMBLAGES OF THE LOWER PILOT SHALE, GREAT BASIN, USA

Ichnodisparity is a classification system for trace fossils which relies on the architectural structure of trace fossils to categorize them and can be used to interpret and compare community structure. The lower Pilot Shale, Famennian in age, was sampled at two localities in western Utah to record Late Devonian infuanal communities and investigate lateral variability in community structure. The two localities, Deadman Wash and Conger Mountain, are approximate 30 km apart and preserve variable trace fossil communities within calcareous shale to fine grained sandstones. Categories of architectural design were used in place of ichnotaxa to determine relative abundance of each category at each locality, and from this the diversity, richness, and evenness as well as the density packing of trace fossils present was calculated. The assemblages from each locality were described using the eight identified categories of architectural designs (Bautois, et al., 2017), and the categories of simple horizontal burrows, passive horizontal burrows, vertical burrows, and paired trackways were found at both localities. Overall the assemblages were similar, although richness at Deadman Wash was higher and the density of vertical burrows was higher at the Conger Mt. locality. Differences in grain size and overall density of trace fossils could be the result of variable sedimentation rate or other depositional conditions that may affect behavior and ultimately preservation in the fossil record. These assemblages preserve conditions before the onset of the Hangenberg extinction event and, therefore, provide a baseline for comparison against post-extinction infaunal communities, as well as other studies of trace fossil ecology in the late Devonian of the Great Basin.