11:00 AM - 11:15 AM
[BCG09-02] Mass extinctions related to global cooling: A case study of the late Ordovician mass extinction using a multi isotope approach
Keywords:Ordovician-Silurian boundary, Stable isotopes, Global cooling
Although the late Ordovician mass extinction was one of the “Big Five” mass extinction events in the Phanerozoic, the rate of species extinction was lower than those of the P-T and K-Pg boundary events . The decline of biodiversity coincided with the onset of the Hirnantian glaciation, the inducing mechanisms for which are still unclear. In this study, isotopic ratios and concentrations of carbon and sulfur were analyzed in the Upper Ordovician to Lower Silurian shales from the Langkawi Islands in Malaysia. The results revealed that the weight ratios of organic carbon and pyritic sulfur (C/S) varied periodically from <1 to ~30. These periodic variations were interrupted by the position of the positive d13C excursion. The excursion was accompanied by C/S ratios <0.1, lower than the minimum values during the periodical variations. Although the C/S ratios varied periodically, the minimum values for each C/S variation cycle gradually increased. This implies that the environmental perturbation recorded as very low C/S ratios repeated high and low intensities, but its fluctuation was attenuated overall.
 Stanley (2010) PNAS 107, 19185-19189.
 McGhee et al. (2011) Geology. 40 (2): 147–150.