11:00 AM - 11:15 AM
[BPT06-02] A study of sulfur and carbon isotopes for understanding environmental changes in the Ordovician-Silurian extinction event
Keywords:Ordovician-Silurian boundary, Carbon stable isotopes, Sulfur stable isotopes, Mass spectrometry
In this study, isotope ratios and concentrations of carbon and sulfur were analyzed for Upper Ordovician to Lower Silurian shale at the Langkawi Islands in Malaysia. The results revealed that the carbon/sulfur ratio (wt%/wt%) varied periodically from less than 1 to ~30. Such periodical variation was interrupted by the position of the positive carbon isotope excursion. Such excursion was accompanied by C/S ratios of less than 0.1, lower than the minimum values during the periodical variation. This means that the depositions of organic carbon and pyritic sulfur occurred in highly anoxic oceans that might have contained hydrogen sulfide in the water column. At the onset of the end-Ordovician mass extinction, which can be characterized by the carbon isotope excursion, highly anoxic waters containing hydrogen sulfide likely expanded to shallow oceans where sand deposition occurred.