Munsterman , D. K., J. H. ten Veen, A. Menkovic, J. Deckers, N. Witmans, J. Verhaegen, S. J. Kerstholt-Boegehold, T. van de Ven, and F. S. Busschers. “An Updated and Revised Stratigraphic Framework for the Miocene and Earliest Pliocene Strata of the Roer Valley Graben and Adjacent Blocks”. Netherlands Journal of Geosciences, vol. 98, Jan. 2020, doi:10.1017/njg.2019.10.