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2. Anderson S. A. (1937) De vulkanske Askelag i Vejgennemskœringen ved Ølst og deres Udbredelse i Danmark. Denmarks Geologiske Undersøgelse, række 2 59.
3. Baadsgaard H. Lerbekmo J. F. (1982) in Numerical dating in stratigraphy, The dating of bentonite beds, ed Odin G. S. (Wiley & Sons), pp 423–440.
4. Rb–Sr and U–Pb dating of bentonites
5. A radiometric age for the Cretaceous–Tertiary boundary based upon K–Ar, Rb–Sr, and U–Pb ages of bentonites from Alberta, Saskatchewan, and Montana