John W.M. Jagt, Werner M. Felder, Rudi W. Dortangs, and Jacques Severijns. “The Cretaceous/Tertiary Boundary in the Maastrichtian Type Area (SE Netherlands, NE Belgium); A Historical Account”. Netherlands Journal of Geosciences, vol. 75, Jan. 1996, pp. 107-18, https://njgjournal.nl/index.php/njg/article/view/12365.