Fig. 5: Biogeochemical responses of biotic extinction and turnover related to the late Cambrian SPICE event.

a Schematic facies model at the end-Marjuman (end-Miaolingian) extinction prior to the SPICE event (Stage I), corresponding to the initial negative δ¹³C shifts pre-SPICE. The extinction of plankton in shallow water regions was potentially linked to a diminished habitat area which was triggered by sea-level regression, or the upwelling of deep waters that were anoxic²⁷ and enriched in ¹²C. The ¹²C enrichment of these waters could stem from the oxidation of methane, released from the decomposition of hydrates, along with other organic substances, including dissolved organic carbon, into CO₂ during the upwelling process⁵⁵. Stage II: Schematic facies model illustrating the role of development of a CO₂ concentrating mechanism (CCM) by phytoplankton in constraining the different responses of the SPICE event in various sedimentary environments during the plankton revolution. b Ranges of δ¹³C_carb values from the SPICE onset to the maximum (SPICE rising limb; left y axis) and the corresponding stratigraphic thickness over which the rising limb of the SPICE is expressed (right y axis). c The differences of the east-west sedimentary facies in the Tarim Basin during the SPICE event and the resulting variations in marine biochemical and redox conditions. PZE: photic zone euxinia. d The CCM was utilized by phytoplankton under the situations of a decrease in pCO₂ and increase in pO₂ during the SPICE event²².