332-7 The Late Pennsylvanian time scale conundrum

Abstract:

The Late Pennsylvanian (307–299 Ma) represents a phase of major climatic and biotic perturbations associated with the final expansion of late Paleozoic ice sheets. A rich spectrum of sedimentary and paleontological records, including the iconic cyclothems of the U.S. basins, is constrained by both radioisotopic and astrochronological data within a conodont biostratigraphic framework. These conditions make the Late Pennsylvanian one of the most promising targets for studies of paleoclimate mechanisms in an icehouse climate. Recent advances in biostratigraphy and geochronology, however, raise new questions regarding the prospect of developing a detailed, integrated time scale. A million-year-scale mismatch is identified between published radioisotopic dates from the Urals and Donbas and a high-resolution astronomical time scale from South China (Naqing). We will evaluate possible solutions including a diachroneity of one of the key biostratigraphic markers (first occurrence of Swadelina subexcelsa), condensation or hiatuses in the radioisotopically calibrated sections, and distortion of the astronomical signal. The most plausible ages for the candidate GSSP markers of the Middle/Late Pennsylvanian (Moscovian/Kasimovian) boundary will be proposed. The results should help to refine the timing of key events such as the Desmoinesian/Missourian vegetation turnover, astronomical-scale CO₂ perturbations, and glacioeustatic records of the U.S. Midcontinent, Illinois and Appalachian basins.

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