High-resolution carbon isotopic records from the Ordovician of South China: Links to climatic cooling and the Great Ordovician Biodiversification Event (GOBE)

Abstract

The Great Ordovician Biodiversification Event (GOBE) represented the largest increase in diversity in the marine biosphere during the Phanerozoic Eon, yet its causes and consequences remain poorly understood. Patterns of isotopic variation in high-resolution δ 13C carb and δ 13C org records from a well-exposed section at Honghuayuan in South China may provide important insights regarding the GOBE. The Honghuayuan isotopic profiles, which can be correlated with C-isotopic records from contemporaneous sections globally, reveal large perturbations to the global carbon cycle during the Ordovician. A + 8‰ increase in δ 13C org values in the Floian implies a large, albeit transient increase in the burial rate of organic matter during the mid-Early Ordovician that may have contributed to climatic cooling and played an important role in triggering the GOBE. A + 4‰ increase in δ 13C carb and high-frequency variation in δ 13C org in the Darriwilian to Sandbian suggest a second episode of elevated organic carbon burial rates accompanied by substantial instability in the global carbon cycle during the late Middle and early Late Ordovician. This pattern may mark the onset of climate changes culminating in the end-Ordovician Hirnantian glaciation and mass extinction event that terminated the GOBE.