Hough, M.L., Shields, G.A., Evins, L.Z., Strauss, H., Henderson, R.A., and Mackenzie, S. (2006) A major sulphur isotope event at c. 510 Ma: a possible anoxia–extinction–volcanism connection during the Early–Middle Cambrian transition? Terra Nova, 18 (4). pp. 257-263.