U-Pb dating of the sedimentary record
University of Geneva,
Web Lecture on June 24, 2021 at 3:00 PM (Paris Time)
U-Pb age determinations provide tie-points of absolute time in the sedimentary record, which then can be used as temporal anchors for other, floating timescales. The most precise and reliable age information comes from the mineral zircon in volcanic ash beds that are interlayered with the sedimentary rocks. Zircon can be dated using the radioactive decay system from 238,235U to 206,207Pb isotopes. With our most sophisticated methods we can presently achieve a precision of 0.02% on a 206Pb/238U date. However, the way to develop the methods to the present precision was a long one, and the way from picking up an ash sample in the field to a precise and reliable age of sedimentation can be a painstaking endeavor as well. This talk tries to outline some of the challenges and assumptions behind our geochronology and will give some insight into the uncertainties both of the analytical approaches as well as of the interpretation of high-precision U-Pb ages.