Speelman, Eveline N.; Reichart, Gert-Jan; de Leeuw, Jan W.; Rijpstra, W. Irene C.; Sinninghe Damste, Jaap S. (2009): Biomarker lipids of the freshwater fern Azolla and its fossil counterpart from the Eocene Arctic Ocean. Elsevier, International, Organic Geochemistry, 40 (5), 628-637, georefid:2010-004122