A NEW FRONTIER IN DEEP-TIME PALEOCLIMATOLOGY REGARDING THE GEOCHRONOLOGY OF PALEOSOLS: A TRIBUTE TO THE CAREER OF STEVEN DRIESE

Steve Driese and I both began our Ph.D. studies as mainstream stratigraphers and sedimentologists at the cusp of the 1980s. Influenced by the bold scientific innovation and artistry of Greg Retallack regarding deep-time paleopedology, Steve’s and my scientific careers intersected with the practice of petrographic soil micromorphology and eventual collaborative work on pedogenic siderites and calibration of their stable isotope fractionations in modern settings. The deep-time paleosol community owes a great debt to Steve for his leadership in helping to propel our discipline into the Earth Sciences mainstream. With our mutual retirements this year, I take this opportunity to offer a vision of future directions for this discipline using recent research results with my colleagues at the University of Kansas. Following a proliferation of geochemical proxies for interpreting paleoclimate from paleosol records over the past two decades, a remaining grand challenge involves the development of refined geologic time-series calibrations of those records. Uranium-lead geochronologists are leaders in this endeavor, with the pioneering works of Troy Rasbury of special note. A recent breakthrough with innovative use of LA-ICP-MS instruments for rapid age determinations of pedogenic/palustrine carbonates promises to overcome the obstacle of dating ancient paleosols. I further note that petrographic cathodoluminescence imaging can help organize a logical workflow for this practice. The conceptual foundation of a burgeoning practice of tephrochronologic correlations of Quaternary cryptotephras is an analogue for this practice in deep-time paleosols. Large zircon populations (n ≥ 300) separated from paleosols can be screened by U-Pb geochronology using LA-ICP-MS instruments to identify cryptotephra populations of volcanogenic zircons that are subsequently used for high-precision U-Pb geochronology using CA-ID-TIMS instrumentation and Bayesian estimates of eruption ages following Keller et al. (2018, Geochem. Persp. Let. 8:31-35). These U-Pb techniques promise to revolutionize how deep-time paleopedologists practice their discipline in the coming years.