G. Kuhlmann, C.G. Langereis, D. Munsterman, R.-J. van Leeuwen, R. Verreussel, J.E. Meulenkamp, and Th.E. Wong. “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, vol. 85, Mar. 2006, pp. 19 -35, doi:10.1017/S0016774600021405.