Progress, problems and prospects: An overview of the Guadalupian Series of South China and North America

Abstract

The Guadalupian Epoch is marked by the formation of the Pangean supercontinent, global sea-level change, rifting and drifting of the Cimmerian continents, formation of large igneous provinces and dramatic biotic changes. A high-resolution biostratigraphic, chemostratigraphic and high-precision geochronologic framework of this critical transition is fundamental to understanding these events. Extensive studies of the latest Cisuralian and Guadalupian Series in both South China and North America reveal the same conodont lineages, but the conodont interval zones based on Jinogondolella within the Guadalupian Series are slightly diachronous. High-precision U-Pb geochronological studies (CA-ID-TIMS method) calibrate the base of the Guadalupian Series (base Roadian) at 273.01 ± 0.14 Ma. A previously reported age from an ash bed overlying the Emeishan flood basalts, 259.51 ± 0.21 Ma, is adopted for the Guadalupian/Lopingian boundary (GLB). Based on recently published geochronology and Bayesian age modeling from the Guadalupian Series, the base of the Capitanian is constrained at 264.28 ± 0.16 Ma and the base of the Wordian is interpolated to be 266.9 ± 0.4 Ma. The Illawarra Reversal is of early-middle Wordian age. Both North America and South China possess a distinct negative δ13Ccarb excursion of 3-5‰ at the latest Kungurian and early Roadian (LK-ER CIE), which coincides with the early stages of a significant 3rd order sea-level rise. The large end-Guadalupian δ13Ccarb negative excursion may have been affected by post-depositional diagenesis or a warming event associated with the Emeishan volcanism. The 87Sr/86Sr ratios in both regions declined from the latest Kungurian to the late Capitanian, but have different ratios and reveal several fluctuations in the middle Guadalupian. Measured δ18Oapatite values suggest that the Delaware Basin was 3-4°C cooler than the eastern Yangtze Block. Analysis of a new high-resolution database of marine taxa indicates only a minor pre-Lopingian diversity drop from 261.04 Ma to 259.98 Ma, which coincides with the peak Emeishan volcanism. The widely-perceived “end-Guadalupian mass extinction” in North America is evidently masked by, and possibly an artefact of, a stratigraphic truncation effect due to rapid lithofacies changes from limestone to laminated evaporites with the closure of the west Texas basins.