No Furongian Biodiversity Gap: Evidence from South China

Abstract

The middle–late Cambrian is a crucial transition interval linking the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE). Previous studies have indicated the Furongian Biodiversity Gap with significantly lower richness and indistinct changes during this time interval. However, in addition to newly discovered deposits and Konservat-Lagerstätten (i.e., Guole Konservat-Lagerstätte in South China), and well-preserved continuous stratigraphic successions, the detailed richness pattern of this interval has emerged, filling the gap between the CE and the GOBE. The high-resolution richness curve of marine invertebrates in South China based on Constrained Optimization analysis revealed several biodiversity events, including three extinctions, two radiations, and one fluctuation interval. The first biotic crisis, the Guzhangian–Paibian extinction, accounted for a 45.0% richness loss and coincided with the global Marjuman extinction event previously identified in the Laurentian trilobite and brachiopod records. The second extinction, the Jiangshanian extinction, resulting in a 55.2% richness loss, can be correlated to the Steptoean–Sunwaptan biomere extinction in Laurentia. Finally, a third extinction mainly affecting cephalopods and conodonts occurred near the Cambrian/Ordovician boundary in South China, immediately followed by the GOBE, a rapid, extraordinary biodiversity increase in the Early and Middle Ordovician. Two radiation intervals have been recognised in the middle–late Drumian and the middle Paibian, respectively, before the first two extinctions. A long-term richness fluctuation started from the latest Jiangshanian until the Cambrian/Ordovician boundary. Some of the events in South China can be identified in other continents, suggesting a global pattern and mechanism. We further discussed the possible relationships between these biotic and environmental changes. The combined Fe speciation change results showed that the species richness seemed to follow the oceanic redox changes. Thus, there is no significant biodiversity gap but marked fluctuations in marine life associated with environmental volatility between the CE and the GOBE in South China.