Keller, Gerta, and Alfonso Pardo. (2004) 2004. “Disaster Opportunists Guembelitrinidae: Index for Environmental Catastrophes”. Marine Micropaleontology 53 (1-2): 83-116. doi:10.1016/j.marmicro.2004.04.012. Reference Link
Pardo, Alfonso, and Gerta Keller. (2008) 2008. “Biotic Effects of Environmental Catastrophes at the End of the Cretaceous and Early Tertiary: Guembelitria and Heterohelix Blooms”. Cretaceous Research 29 (5-6): 1058-73. doi:10.1016/j.cretres.2008.05.031. Reference Link
Pardo, Alfonso, Gerta Keller, and Hedi Oberhaensli. 1999. “Paleoecologic and Paleoceanographic Evolution of the Tethyan Realm During the Paleocene-Eocene Transition”. The Journal of Foraminiferal Research 29: 37-57. Referenced from jfr.geoscienceworld.org: Paleoecologic and paleoceanographic evolution of the Tethyan realm during the Paleocene-Eocene transition. Reference Link
Keller, Gerta, and Alfonso Pardo. (2004) 2004. “Age and Paleoenvironment of the Cenomanian–Turonian Global Stratotype Section and Point at Pueblo, Colorado”. Marine Micropaleontology 51 (1-2): 95-128. doi:10.1016/j.marmicro.2003.08.004. Reference Link
Tantawy, AAAM, Gerta Keller, and Alfonso Pardo. (2009) 2009. “Late Maastrichtian Volcanism in the Indian Ocean: Effects on Calcareous Nannofossils and Planktic Foraminifera”. Palaeogeography, Palaeoclimatology, Palaeoecology 284 (1-2): 63-87. doi:10.1016/j.palaeo.2009.08.025. Reference Link