Quantitative radiometric and biostratigraphic calibration of the Pennsylvanian-Early Permian (Cisuralian) time scale and pan-Euramerican chronostratigraphic correlation

Abstract

A quantitative biostratigraphic and radiometric calibration is presented for the Pennsylvanian through Early Permian global time scale, based upon high-precision, isotope dilution–thermal ionization mass spectrometer (ID-TIMS) U-Pb zircon ages for interstratified ash beds in the parastratotype sections of the southern Urals of Russia. Twenty-four ash-bed ages in three outer ramp and basinal sections of the Pre-Uralian foredeep bracket the biotic definitions of global stages and regional substages from the base of the Upper Pennsylvanian Kasimovian Stage to the base of the Lower Permian Artinskian Stage; four additional ash-bed ages in two sections of the eastern slope of the Urals constrain the global Bashkirian and Serpukhovian Stages. Quantitative stratigraphic methods (CONOP9) are applied to a compilation of over 2000 bioevents in 22 stratigraphic sections supplemented by our dated volcanic horizons to refine the Pennsylvanian–Early Permian global time scale. Significant shifts in the duration of several stages are demonstrated, ranging from one to six million years, compared with prior estimates. The unprecedented density of radiometric calibration points for the Pennsylvanian–Permian transition provides a high-resolution (∼0.1-Ma) global chronostratigraphic standard for testing and improving biostratigraphic correlations across Euramerica. We integrate radiometric ages, biostratigraphic correlation, and cyclostratigraphic tuning of major cyclothems to the long-period (404-ka) eccentricity cycle to elucidate the tempo, magnitude, and forcing of eustatic changes and cyclothemic deposition associated with the waxing and waning of Gondwanan ice sheets, and establish a pan-Euramerican chronostratigraphic framework for most of Pennsylvanian and Early Permian time.