Carbon-isotope stratigraphy recorded by the Cenomanian-Turonian Oceanic Anoxic Event: correlation and implications based on three key localities by Tsikos, H, Jenkyns, H, Walsworth-Bell, B, Petrizzo, MR, Forster, A, Kolonic, S, Erba, E, Silva, I, Baas, M, Wagner, T, Damste, J