Blancan

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The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,808,000 years BP, a period of 2.942 million years.[1] It is usually considered to start in the early-mid Pliocene Epoch and end by the early Pleistocene.[2] The Blancan is preceded by the Hemphillian and followed by the Irvingtonian NALMA stages.

As usually defined, it corresponds to the mid-Zanclean through Piacenzian and Gelasian stages in Europe and Asia. In California, the Blancan roughly corresponds to the mid-Delmontian through Repettian and Venturian to the very early Wheelerian. The Australian contemporary stages are the mid-Cheltenhamian through Kalimnan and Yatalan. In New Zealand, the Opoitian starts at roughly the same time and the Blancan is further coeval with the Waipipian and Mangapanian stages to the early Nukumaruan. Finally, in Japan the Blancan starts coeval with the late Yuian, runs alongside the Totomian and Suchian and ends soon after the start of the Kechienjian.

Dating issues[edit]

The start date of the Blancan has not been fully established. There is general agreement that it is between 4.9[3] and 4.3 mya (million years ago).[4] The often-cited GeoWhen database places it at 4.75 mya.[1]

There is even stronger disagreement about the end of the Blancan. Some stratigraphers argue for the 1.808 mya date that corresponds better with the end of the Pliocene and the start of the Pleistocene (1.808 mya). This conforms with the extinction of Borophagus, Hypolagus, Paenemarmota, Plesippus, Nannippus, and Rhynchotherium faunal assemblage between 2.2 and 1.8 mya.[2] Other paleontologists find continuity of the faunal assemblages well into the Pleistocene, and argue for an end date of 1.2 mya. This corresponds with the extinction of stegomastodons and related species and the appearance of mammoths in southern North America.[5]

Fauna[edit]

The middle of the Blancan, about 2.7 mya, is when the land bridge connection between North and South America was reestablished and taxa like sloths and glyptodonts appeared in North America at the height of the Great American Interchange.[6]

References[edit]

  1. ^ a b Blancan North American Stage. GeoWhen Database. Version 1.1.0. Retrieved 2007-NOV-09.
  2. ^ a b Lundelius, E.L. Jr. et al. (1987): The North American Quaternary Sequence. In: Woodburne, Michael O. (ed.): Cenozoic mammals of North America: geochronology and biostratigraphy: 211–235. University of California Press, Berkeley. ISBN 0-520-05392-3
  3. ^ Lindsay, Everett et al. (2002). "Recognition of the Hemphillian/Blancan boundary in Nevada". J. Vertebr. Paleontol. 22 (2): 429–442. doi:10.1671/0272-4634(2002)022[0429:ROTHBB]2.0.CO;2. 
  4. ^ Cassiliano, Michael L. (1999). "Biostratigraphy of Blancan and Irvingtonian mammals in the Fish Creek–Vallecito Creek section, southern California, and a review of the Blancan-Irvingtonian boundary". J. Vertebr. Paleontol. 19 (1): 169–186. doi:10.1080/02724634.1999.10011131. 
  5. ^ Tedford, Richard H. (1981). "Mammalian biochronology of the late Cenozoic basins of New Mexico". Geological Society of America Bulletin 92 (12): 1008–1022. doi:10.1130/0016-7606(1981)92<1008:MBOTLC>2.0.CO;2. 
  6. ^ Woodburne, Michael O. & Swisher, C.C. III (1995): Land mammal high-resolution geochronology, intercontinental overland dispersals, sea level, climate, and vicariance. Society for Economic Paleontology and Mineralogy Special Publications 54: 335–364. ISBN 1-56576-024-7
  7. ^ a b Wetmore, Alexander (1937). "The Eared Grebe and other Birds from the Pliocene of Kansas". Condor 39 (1): 40. 
  8. ^ Feduccia, J. Alan; Ford, Norman L. (1970). "Some birds of prey from the Upper Pliocene of Kansas". Auk 87 (4): 795–797. doi:10.2307/4083714. 

Further reading[edit]

See also[edit]

Neogene Period
Miocene Pliocene
Aquitanian |Burdigalian
Langhian | Serravallian
Tortonian | Messinian
Zanclean | Piacenzian
Quaternary
Pleistocene Holocene
Early | Middle | Late Preboreal | Boreal |
Atlantic | Subboreal | Subatlantic