Niels Stentoft, Peter Frykman, Kaare L. Rasmussen, and Christian J.W. Koch. 1991. “EDTA-Insoluble Residues from the Zechstein Ca-2 Unit (Late Permian), the L0gumkloster-1 Well, Denmark”. Netherlands Journal of Geosciences, January, 115-28. https://njgjournal.nl/index.php/njg/article/view/12792.