HIGH-PRECISION U-Pb ZIRCON AGE CONSTRAINTS ON THE CARBONIFEROUS-PERMIAN BOUNDARY IN THE SOUTHERN URALS STRATOTYPE

Abstract

Volcanic-ash beds within fossiliferous strata of the southern Uralian foredeep of Russia have been dated by the high-precision ID-TIMS U Pb zircon method, to constrain the age of the Carboniferous Permian transition. The stratigraphic section exposed at the Usolka locality, an auxiliary stratotype for the Carboniferous Permian boundary, contains a detailed multi-taxa biostratigraphy with a well-resolved boundary succession tied to the Global Stratotype Section and Point (GSSP) at Aidaralash Creek (Kazakhstan). Four tuffs bracketing the Carboniferous Permian transition in the Usolka section closely constrain the age of the boundary to 298.90 + 0.31/- 0.15 Ma (2sigma), including both analytical and stratigraphic uncertainty. These data substantially improve the calibration of the geologic time scale in the Late Paleozoic, and presage the radiometric age resolution possible for the late Carboniferous and early Permian stages through continued analysis of ash beds in the southern Urals stratotypes. By stabilizing the numeric age for the base of the Permian, these data also provide an important link between the timing of Permo-Carboniferous glaciation in Gondwana and its far-field climatic and sedimentological consequences in Euramerica.