H.W. Oosterink, Th. Simon, H. Hagdorn, and H. Winkelhorst. “Geo (Im) Pulse A Subrosion Pipe Fill in the Lower Muschelkalk, Winterswijk Quarry, Eastern Netherlands”. Netherlands Journal of Geosciences, vol. 85, Dec. 2006, pp. 293 -97, doi:10.1017/S0016774600023088.