Astronomical climate changes trigger Late Devonian bio- and environmental events in South China

One of the five great mass extinctions of the Phanerozoic is the Frasnian-Famennian (Fsbnd F) mass extinction, for which the causes have not yet been identified. In this study, cyclostratigraphic analysis of two Fsbnd F transition sections was carried out in South China: the Yangdi section, a marine slope facies, and the Lali section, a marine basin facies. Paleoclimate proxy data collected at high resolution along these sections include magnetic susceptibility and X-ray fluorescence geochemistry (Ca and Fe concentrations). Time series analysis and modeling of the proxy data reveal that frequencies comparable to those of the Earth's long and short orbital eccentricity, obliquity, and precession index characterize the two successions. Metronomic 405-kyr long orbital eccentricity cycles identified along the two sections were used to construct a floating astronomical time scale across the Fsbnd F transition, revealing that 1000 kyr separates the Lower and Upper Kellwasser horizons (LKH and UKH), and ~1600 kyr separates the maximum values of the LKH and UKH δ¹³C excursions. The estimated duration of the UKH is 150 kyr, during which the first, second, and third extinctions of the Fsbnd F biotic crisis lasted 120 kyr, 20 kyr, and 10 kyr, respectively. Sedimentary noise models of the magnetic susceptibility and Ca concentration time series indicate that changes in sedimentary noise correspond to sea level variations. Modeling suggests that the long orbital eccentricity cycles controlled sea surface temperatures, and that third-order eustatic changes were forced by the combined orbital eccentricity and obliquity variations. Finally, we propose an "astronomical climate change" model as a defining mechanism of the Fsbnd F biotic crisis.