G. Kuhlmann, C.G. Langereis, D. Munsterman, R.-J. van Leeuwen, R. Verreussel, J.E. Meulenkamp, & Th.E. Wong. (2006). Integrated chronostratigraphy of the Pliocene-Pleistocene interval and its relation to the regional stratigraphical stages in the southern North Sea region. Netherlands Journal of Geosciences, 85, 19 - 35. https://doi.org/10.1017/S0016774600021405