PRESERVATIONAL BIASES IN TRACES AND BODY FOSSILS OF WESTERN UNITED STATES PRECAMBRIAN-CAMBRIAN BOUNDARY-SPANNING UNITS

The final ten million years of the Precambrian contains the transition from the classic Ediacarans to a worm-dominated fauna, the first appearance of a dominant modernesque fauna in the marine fossil record. A lack of stratigraphic sections containing complete transitioning faunal assemblages through the terminal Ediacaran impedes our ability to interpret true ecologically-driven changes occurring during this key moment in evolutionary history. The absence of a particular fossil fauna, whether body or trace, could be equally attributed to the inability to preserve the organism or the preservation of an environment in which the organism did not live. When multiple temporally congruent sections exist, but each contains only a subset, varied between sites, of the known fauna, it is difficult to understand the impact of the ecological and environmental changes on the total faunal community. Such a situation currently exists within the western United States Deep Spring and Wood Canyon Formations, with certain sections only containing body fossils and others containing dominantly trace fossils and occasional classic Ediacarans. Here, we present a sedimentological, paleontological, and taphonomic comparison between the trace-dominated Wood Canyon sediments from Boundary Canyon and Chicago Pass and White-Inyo Deep Spring in California, and the body fossil deposits from the Wood Canyon Johnnie section and the Deep Spring at Mount Dunfee in Nevada. The sections are temporally correlative and each present variation in sedimentology and fossil occurrences over a fairly large geographic extent. Through comparing the host sedimentology, we hope to present a reasonable model for predicting the level of preservation quality and potential fossil occurrences from additional late Ediacaran units.