Selandian

The Selandian is in the geologic timescale an age or stage in the Paleocene. It spans the time between 61.6 and 59.2 Ma. It is preceded by the Danian and followed by the Thanetian.[2] Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "Middle Paleocene".

System/
Period		 Series/
Epoch		 Stage/
Age		 Age (Ma)
Neogene Miocene Aquitanian younger
Paleogene Oligocene Chattian 23.0 27.8
Rupelian 27.8 33.9
Eocene Priabonian 33.9 37.8
Bartonian 37.8 41.2
Lutetian 41.2 47.8
Ypresian 47.8 56.0
Paleocene Thanetian 56.0 59.2
Selandian 59.2 61.6
Danian 61.6 66.0
Cretaceous Upper/
Late		 Maastrichtian older
Subdivision of the Paleogene Period
according to the ICS, as of 2019.[1]

Stratigraphic definition

The Selandian was introduced in scientific literature by Danish geologist Alfred Rosenkrantz in 1924. It is named after the Danish island of Zealand (Danish: Sjælland) given its prevalence there.[3]

The base of the Selandian is close to the boundary between biozones NP4 and NP5. It is slightly after the first appearances of many new species of the calcareous nanoplankton genus Fasciculithus (F. ulii, F. billii, F. janii, F. involutus, F. tympaniformis and F. pileatus) and close to the first appearance of calcareous nanoplankton species Neochiastozygus perfectus. At the original type location in Denmark the base of the Selandian is an unconformity. The official GSSP was established in the Zumaia section (43° 18'N, 2° 16'W) at the beach of Itzurun in the Basque Country, northern Spain.[4]

The GSSP marking the lower boundary of the Selandian at Itzurun, Spain

The top of the Selandian (the base of the Thanetian) is laid at the base of magnetic chronozone C26n.

The Selandian stage overlaps with the lower part of the Tiffanian North American Land Mammal Age, the Peligran, Tiupampan and lower Itaboraian South American Land Mammal Ages and part of the Nongshanian Asian Land Mammal Age. It is coeval with the lower part of the Wangerripian stage from the Australian regional timescale.

The start of the Selandian represents a sharp depositional change in the North Sea Basin, where there is a shift to siliciclastic deposition due to the uplift and erosion of the Scotland-Shetland area after nearly 40 million years of calcium carbonate deposition.[5] This change occurs at the same time as the onset of a foreland basin formation in Spitsbergen due to compression between Greenland and Svalbard,[6] suggesting a common tectonic cause that altered the relative motions of the Greenland Plate and the Eurasian Plate. This plate reorganisation event is also manifest as a change in seafloor spreading direction in the Labrador Sea around this time.[7]

Fauna and Flora

The fauna of the Selandian consisted of giant snakes (Titanoboa),[8] crocodiles, champsosaurs, Gastornithiformes[9] Owls; while the mammalian fauna was composed of a few archaic forms of mammals, such as Mesonychids, Pantodonts, primate relatives Plesiadapids, and Multiberculates.

The flora was composed of cacti, ferns, angiosperms, and palm trees.

References
  1. "International Chronostratigraphic Chart". International Commission on Stratigraphy.
  2. International Commission on Stratigraphy 2017
  3. Selandien, Den Store Danske Encyklopædi
  4. See for example Arenillas et al. (2008) or Bernaola et al. (2009) for a description of the Danian-Selandidan boundary
  5. Clemmensen A, Thomsen E (2005). "Palaeoenvironmental changes across the Danian–Selandian boundary in the North Sea Basin". Palaeogeography, Palaeoclimatology, Palaeoecology. 219 (3–4): 351–394. doi:10.1016/j.palaeo.2005.01.005.
  6. Jones MT, Augland LE, Shephard GE, Burgess SD, Eliassen GT, Jochmann MM, Friis B, Jerram DA, Planke S, Svensen HH (July 2017). "Constraining shifts in North Atlantic plate motions during the Palaeocene by U-Pb dating of Svalbard tephra layers". Scientific Reports. 7 (1): 6822. doi:10.1038/s41598-017-06170-7. PMC 5533774. PMID 28754976.
  7. Oakey GN, Chalmers JA (2012). "A new model for the Paleogene motion of Greenland relative to North America: Plate reconstructions of the Davis Strait and Nares Strait regions between Canada and Greenland". Journal of Geophysical Research: Solid Earth. 117 (B10): B10. doi:10.1029/2011jb008942.
  8. Kwok R (4 February 2009). "Scientists find world's biggest snake". Nature News. doi:10.1038/news.2009.80.
  9. See for example Koeberl C, MacLeod KG, eds. (2002). Catastrophic events and mass extinctions: Impacts and beyond. Geological Society of America. pp. 303–4.

Further reading
  • Arenillas I, Molina E, Ortiz S, Schmitz B (2008). "Foraminiferal and δ13C isotopic event-stratigraphy across the Danian-Selandian transition at Zumaya (northern Spain): chronostratigraphic implications". Terra Nova. 20: 38–44. doi:10.1111/j.1365-3121.2007.00784.x.
  • Bernaola G, Martín-Rubio M, Baceta JI (2009). "New high resolution calcareous nannofossil analysis across the Danian-Selandian transition at the Zumaia section: comparisons with South Tethys and Danish sections". Geologica Acta. 7 (1–2): 79–92.
  • Gradstein FM, Ogg JG, Smith AG (2004). A Geologic Time Scale. Cambridge University Press.
  • Rosenkrantz A (March 1921). "En ny københavnsk Lokalitet for forsteningsførende Paleocæn". Meddelelser fra Dansk Geologisk Forening (in Danish). 5: 1–10.
  • Rosenkrantz A (1924). "De københavnske Grønsandslag og deres Placering i den danske Lagrække". Meddelelser fra Dansk Geologisk Forening (in Danish). 6: 1–39.

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