Unlocking Cambrian Clastic Sedimentary Successions with Tandem Detrital Zircon Geochronology and Bayesian Age Modeling

Rocks of the Cambrian Period (539-485 Ma) record dramatic changes in Earth systems including atmospheric oxygenation, large magnitude perturbations to the carbon cycle, and the Cambrian Explosion of animal life, all within a series of transgressions of sea level onto continental margins across the Great Unconformity. While pioneering 20th century U-Pb zircon geochronology and subsequent carbon isotope stratigraphy correlation frameworks revolutionized our framing of the lower Cambrian explosion of animal diversity and disparity, remarkably few opportunities for further calibration of the Cambrian have arisen in the intervening decades. Southwest Laurentia holds key paleontological and biogeochemical records of Cambrian environments in transgressive fluvio-marine systems exposed from southern Arizona and New Mexico to northern Utah, yet due to a lack of dateable volcanic horizons these records have not played a significant historical role in understanding the timing and tempo of Cambrian Earth systems. Recent work has unlocked the potential of these sections using tandem in situ and isotope dilution U-Pb geochronology of detrital zircons and novel Bayesian age models, while affirming their global significance via renewed efforts in U-Pb zircon ash bed geochronology in the classic Avalonian sequences of Atlantic Canada. These geochronologic and chronostratigraphic insights from Laurentia and Avalonia necessitate reallocations of time within the global Cambrian Period that have implications for the age of the Precambrian-Cambrian boundary, the tempo of biological change, perturbations to ocean and atmospheric composition, and the drivers of marine transgression.