NEW ID-TIMS U-PB ZIRCON AGES BRACKETING THE ASSELIAN-SAKMARIAN STAGE BOUNDARY (LOWER PERMIAN), SOUTHERN URALS—RUSSIA, KAZASKHSTAN

Abundant interstratified volcanic tuffs within a detailed multi-taxa biostratigraphic framework for Late Pennsylvanian-Cisuralian (Early Permian) marine sections of the southern Urals provide the opportunity to calibrate the absolute ages and durations of the global stages and biozonal subdivisions of this geological transition, which holds one of the Phanerozoic's major climate regime changes. A refined Carboniferous-Permian (C-P) boundary age of 298.2±0.2 Ma is based on statistically indistinguishable bracketing ash beds from the Usolka section. New ID-TIMS U-Pb zircon ages (weighted mean ²⁰⁶Pb/²³⁸U dates of equivalent annealed and chemically abraded single zircons with no rejected outliers) of 296.2±0.2 Ma and 290.0±0.4 Ma have been obtained for two ash beds 12.5 meters below and above the Asselian-Sakmarian boundary, respectively, in the Usolka section. These new ages combined with sedimentologic and biostratigraphic data are being used to refine the chronostratigraphic calibration of the Composite Reference Section for the southern Urals stratotypes.

With this high-resolution framework we can anticipate unprecedented temporal constraints on: the rates of sedimentation and sea-level change in various locations around the world; accurate reconstructions of the full range of variability of the Late Paleozoic climate systems; the relations between marine and terrestrial geologic records; spatial and temporal patterns of extinction events and the rates of ecological recovery and biodiversification following such events; and the timing, duration, and synchroneity of tectonic activity associated with the final assembly and early modification of Pangaea.