Fig. 1. New chemostratigraphic columns of carbon and nitrogen isotope compositions in Doushantuo Member IV.

a Carbonate carbon isotopes. b Organic carbon isotopes. c Carbonate and organic carbon isotopes difference. d Sedimentary nitrogen isotopes. e Total organic carbon content. Data are classified by depositional environments and, where applicable, shown in comparison with published data^{5,26,28–30,68}. *U − Pb age of 551.1 ± 0.7 Ma⁶⁹. Vertical dashed lines from left to right show Peedee belemnite, isotopic fractionation imparted to biomass by primary producers typically around −27‰, photosynthetic range 22–32‰ based on compilations of Δ¹³C_carb-org throughout the Phanerozoic⁷⁰, and lastly δ¹⁵N for atmospheric N₂.