Van den Bosch, M. & Cadée, M.C. & Janssen, A.W. (1975)
Lithostratigraphical and biostratigraphical subdivision of Tertiary deposits (Oligocene - Pliocene) in the Winterswijk - Almelo region (eastern part of the Netherlands). Scripta Geologica, 29, 1–167
Janssen, A.W. & Van den Bosch, M. & von der Hocht, F. (1988)
Age determination of a Tertiary deposit at Kervenheim in the Lower Rhine District, in connection with the find of a whale skeleton (F.R.G., Nordrhein-Westfalen). Rijksmuseum van Geologie en Mineralogie, 124, 1–8