The top of the Olduvai Subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, hominin sites and Paleolakes Drilling Project (HSPDP) by Sier, M, Langereis, C, Dupont-Nivet, G, Feibel, C, Joordens, J, van der Lubbe, J, Beck, C, Olago, D, Cohen, A