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

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 delta C-13(carb) and delta C-13(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 parts per thousand increase in delta C-13(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 parts per thousand increase in delta C-13(carb) and high-frequency variation in delta C-13(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. (C) 2010 Elsevier B.V. All rights reserved.