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Stratigraphy, fossils, and age of sediments at the upper pit of the Lost Chicken gold mine: new information on the late Pliocene environment of east central Alaska

Published online by Cambridge University Press:  20 January 2017

John V. Matthews Jr.*
Affiliation:
Ohana Productions, 1 Red Maple Ln, Hubley, Nova Scotia B3Z 1A5, Canada
J. A. Westgate
Affiliation:
Dept. of Geology, University of Toronto, Toronto, Ontario M5S 3B1, Canada
Lynn Ovenden
Affiliation:
RR 3, Casselman, Ontario K0A 1M0, Canada
L. David Carter
Affiliation:
201 Libby St., Sequim, WA 98382, USA
Thomas Fouch
Affiliation:
The Geological Society of America, P.O. Box 9140, Boulder, CO 80301-9140, USA
*
*Corresponding author. E-mail address:[email protected] (J.V. Matthews).

Abstract

The “upper pit” at the Lost Chicken placer gold mine in east central Alaska contains fossils that provide information on the flora and insect fauna of interior Alaska just before the onset of global cooling at 2.5 myr. Fossils come from sediments interbedded with the Lost Chicken tephra (dated at 2.9 ± 0.4 myr—early Late Pliocene) and portray the floodplain and valley of a small creek within a region dominated by a coniferous forest richer in genera and species than the present one. Climate was wetter and less continental, and there was probably little or no permafrost. At least one other Pliocene tephra (the Fortymile tephra) occurs at the site and is also associated with plant and insect fossils. Among these fossils are extinct plants and insects like those found at other Tertiary sites in northern Canada and Alaska. The Lost Chicken sequence is the same age as the Beaufort Formation on Meighen Island, more than 1000 km to the north. Like Lost Chicken, Meighen Island sediments contain fossils representing a diverse boreal environment. This shows that the latitudinal climate gradient during early Late Pliocene time was shallower than at present and the boreal forest had a far greater latitudinal span than now.

Type
Research Article
Copyright
University of Washington

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