NEW AGE CONSTRAINTS FOR THE BASAL CAMBRIAN PERIOD: GEOCHRONOLOGY OF THE LOWER WOOD CANYON FORMATION, NEVADA, USA

The tempo of the radiation of modern clades of metazoans in the early Cambrian remains uncertain. Here, we present high-precision U-Pb zircon maximum depositional ages for the lower member of the Wood Canyon Formation in Nevada that calibrate the first appearance of basal Cambrian index ichnotaxa within these strata, as well as carbon isotope perturbations that are used to globally correlate small shelly fossil records via chemostratigraphy. The results suggest that the Ediacaran-Cambrian boundary is significantly younger than previously recognized, consistent with an explosive Cambrian radiation of animals. The improved age model for Death Valley stratigraphy also constrains the timing of the Sauk transgression, which is associated with the development of the Great Unconformity in western Laurentia.