Torbjorn E. Tornqvist, Henk J.T. Weerts, and Henk J.A. Berendsen. “Definition of Two New Members in the Upper Kreftenheye and Twente Formations (Quaternary, the Netherlands): A Final Solution to Persistent Confusion?”. Netherlands Journal of Geosciences, vol. 72, Jan. 1994, pp. 251-64, https://njgjournal.nl/index.php/njg/article/view/12513.