G.F.W. HERNGREEN; C. HARTKOPF-FRODER; G.H.J. RUEGG. Age and depositional environment of the Kuhfeld Beds (Lower Cretaceous) in the Alstatte Embayment (W Germany, E Netherlands). Netherlands Journal of Geosciences, v. 72, p. 375-391, 1 Jan. 1994.