ABSTRACT

During the Ordovician, huge biological revolutions and environmental changes happened in Earth’s history, including the Great Ordovician Biodiversification Event, global cooling and so on, but the cause of these events remains controversial. Herein, we conducted a paired carbon iso-topic analysis of carbonate (d¹³C_carb) and organic matter (d¹³C_org) through the Ordovician in the Qiliao section on the Yangtze platform of South China. Our results showed that the d¹³C_carb trend of the Qiliao section can be correlated with local and global curves. The d¹³C_org trend seems is less clear than the d¹³C_carb trend for stratigraphic correlations, but some d¹³C_org positive excursion sin the Middle and Upper Ordovician may be used for correlation studies. These carbon isotopic records may have global significance rather than local significance, revealing several fluctuations to the global carbon cycle during the Ordovician. Several known d13Ccarb and d13Corg negative and positive excursions have been recognised in this study, including the early Floian Negative Inorganic Carbon (d¹³C_carb) Excursion (EFNICE), as well as the early Floian Positive Organic Carbon(d¹³C_carb) Excursion, the mid-Darriwilian Inorganic Carbon (d¹³C_carb and d¹³C_org) Excursion (MDICE),and the early Katian Guttenberg Inorganic Carbon (d¹³C_carb and d¹³C_org) Excursion (GICE). These positive excursions and a smooth decline trend of d¹³C_org values during the early to mid-Floian may imply multiple episodes of enhanced organic carbon burial that began at the early Floian stage, probably resulting in further decline in atmospheric pCO₂ and then global cooling.

KEYWORDS

carbon isotope stratigraphy; Ordovician; positive excursion; global cooling; Yangtze platform