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  • Cited by 5
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    This chapter has been cited by the following publications. This list is generated based on data provided by CrossRef.

    Lawver, Daniel R. and Boyd, Clint A. 2018. An avian eggshell from the Brule Formation (Oligocene) of North Dakota. Journal of Vertebrate Paleontology, p. 1.

    Korth, William W. 2018. Review of the marsupials (Mammalia: Metatheria) from the late Paleogene (Chadronian–Arikareean: late Eocene–late Oligocene) of North America. PalZ, Vol. 92, Issue. 3, p. 499.

    Kent-Corson, Malinda L. Mulch, Andreas Graham, Stephan A. Carroll, Alan R. Ritts, Bradley D. and Chamberlain, C. Page 2010. Diachronous isotopic and sedimentary responses to topographic change as indicators of mid-Eocene hydrologic reorganization in the western United States. Basin Research,

    Worley-Georg, Marie P. and Eberle, Jaelyn J. 2006. Additions to the Chadronian Mammalian fauna, Florissant Formation, Florissant Fossil Beds National Monument, Colorado. Journal of Vertebrate Paleontology, Vol. 26, Issue. 3, p. 685.

    Wesley, G. D. and Flynn, J. J. 2003. A revision of Tapocyon (Carnivoramorpha), including analysis of the first cranial specimens and identification of a new species. Journal of Paleontology, Vol. 77, Issue. 04, p. 769.

  • Print publication year: 1996
  • Online publication date: July 2010

14 - Magnetostratigraphy and biostratigraphy of the Eocene-Oligocene transition, southwestern Montana



Detailed magnetostratigraphic and biostratigraphic studies of Eocene-Oligocene deposits in southwestern Montana have greatly refined the dating of the fossil mammal assemblages known from the region. In the Jefferson Basin, the middle Chadronian Pipestone Springs l.f. correlates with Chrons C15r to C16r1 (35.0-35.5 Ma). The assemblages known from the middle to late(?) Chadronian Little Pipestone Creek localities correlate at least in part with Chrons C15r to C16n1 (35.0-35.4 Ma). The late Chadronian West Easter Lily l.f. and the succeeding early Orellan Easter Lily l.f. span much of Chron C13r (33.5-34.3 Ma). In the Beaverhead Basin, the early Chadronian McCarty's Mountain fauna correlates with Chrons C16r1 to C17n1 (35.5-36.7 Ma). The late Duchesnean Diamond O Ranch l.f. may correlate with part of the long episode of normal polarity during Chron C17n. In the Sage Creek Basin, the late Uintan Dell beds have produced the stratigraphically successive Douglass Draw and Hough Draw local faunas, both of which appear to fall in Chron C18r (40.2-41.0 Ma). The Matador Ranch and Cook Ranch local faunas from the stratigraphically higher Cook Ranch Formation are correlated with the Orellan part of Chron C12r (32.0-33.0 Ma).

The mammalian local faunas of southwestern Montana strongly reflect the significant faunal provincialism that characterized western North America during the Eocene-Oligocene transition. A varying percentage (generally 20-40%) of the mammalian species known from the late Uintan through late Orellan local faunas of the region appear to have been endemic to southwestern Montana.

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The Terrestrial Eocene-Oligocene Transition in North America
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