A 20-million-year reconstruction to decipher the enigmatic Cambrian extinction – Ordovician biodiversification transition

The late Cambrian extinction – Early Ordovician biodiversification represents one of the crucial lower Paleozoic biological changes. However, the mechanisms responsible for this transition remain poorly understood. Here, we reconstructed the paleoenvironmental changes based on a model that integrated the atmospheric-oceanic-biological inputs and provided the first detailed assessment of the Cambro-Ordovician biological turnover. The results show depositional environments evolved into extremely sulfidic conditions with lower nutrient inputs and more restricted water circulation from the Miaolingian to early Furongian, leading to the Steptoean Positive Carbon Isotope Excursion event. The intense volcanic activity in the early Jiangshanian appears to be responsible for the recurrent bio-calamity. Later in the mid-late Furongian (mid-Jiangshanian to Stage 10), enhanced terrestrial weathering contributed to the Earth's cooling and higher inputs of terrestrial nutrients, beneficial to the subsequent biological recovery. In the Early Ordovician and despite reduced terrestrial nutrient input, massive oceanic water upwelling alleviated sulfidic conditions and brought nutrients, laying the foundation for the Great Ordovician Biodiversification Event.