Fig. 2: Nickel isotopic compositions and Ni contents of black shales in the Buchanan Lake section.

Error bars represent 2 s.d. The C-isotope chemostratigraphy is from ref. ⁵ and shaded areas refer to fly coal ash loading events reported in ref. ⁵. Palaeo-redox conditions are from refs. ^21,22 and U-Pb age for the EPME horizon is from ref. ²⁷.