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The 'Blancan North American Stage' on the geologic timescale is the length of time, stage, from 4,750,000 to 1,808,000 years BP.^[1][2] It is based upon North American faunal assemblages and is consistent with North American Land Mammal Ages (NALMA). The Blancan is preceded by the Hemphillian stage and followed by the Irvingtonian.
The Blancan is a stage within the Pliocene epoch. It corresponds to the mid-Zanclean, through Piacenzian and Gelasian stages in Europe and Asia, and ends with the start of the Pleistocene. In California, the Blancan roughly corresponds to the mid-Delmontian to very early Wheelerian.

Contents

Dates

Notes

References

Dates

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.^[4] The often-cited GeoWhen database places it at 4.75 mya.
The middle of the Blancan, about 2.7 mya, is when the land bridge connection between North and South America was reestablished and species like the sloths and glyptodonts, appeared in North America.^[5]
There is disagreement about the end of the Blancan. Some stratigraphers argue for the 1.808 mya date that corresponds to the end of the Pliocene and the start of the Pleistocene. This conforms with the extinction of the Borophagus, Hypolagus, Paenemarmota, Equus (Plesippus), Nannippus, and Rhynchotherium faunal assemblage between 2.2 and 1.8 mya.^[6] 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 stegomastodon and related species and the appearance of mammoths in southern North America.^[7]

Notes

1. GeoWhen Database - Blancan
2. Lourens, L. ''et al.'' (2004) "The Neogene Period" In: Gradstein, F., Ogg, J., Smith, A.G. (eds.) (2004) ''A Geologic Time Scale 2004'' Cambridge University Press, Cambridge, ISBN 0-521-78142-6
3. Lindsay, Everett ''et al.'' (2002) "Recognition of the Hemphillian/Blancan boundary in Nevada" ''Journal of Vertebrate Paleontology'' 22(2): pp. 429–442
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" ''Journal of Vertebrate Paleontology'' 19(1): pp. 169–186
5. Woodburne, Michael O. and Swisher, C. C., III (1995) "Land mammal high-resolution geochronology, intercontinental overland dispersals, sea level, climate, and vicariance" In: Berggren, William A. ''et al.'' (eds.) (1995) ''Geochronology, time scales, and global stratigraphic correlation'' Society for Economic Paleontology and Mineralogy, Special Publication 54, Tulsa, Oklahoma, pp. 335–364 ISBN 1-56576-024-7
6. Lundelius, E. L., Jr. ''et al.'' (1987) "The North American Quaternary Sequence" In Woodburne, Michael O. (ed.) (1987) ''Cenozoic mammals of North America: geochronology and biostratigraphy'' University of California Press, Berkeley, pp.211–235, ISBN 0-520-05392-3
7. Tedford, Richard H. (1981) "Mammalian biochronology of the late Cenozoic basins of New Mexico" ''Geological Society of America Bulletin'' 92(12): pp. 1008–1022

References

★ Morgan, Gary S. and Lucas, Spencer G. (2003) "Mammalian Biochronology of Blancan and Irvingtonian (Pliocene and Early Pleistocene) Faunas from New Mexico" ''Bulletin of the American Museum of Natural History'' 279(1): pp. 269–320