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Deglaciation and Postglacial Timberline in the San Juan Mountains, Colorado

Published online by Cambridge University Press:  20 January 2017

P.E. Carrara ,
W.N. Mode ,
Meyer Rubin  and
S.W. Robinson
P.E. Carrara
Affiliation:
United States Geological Survey, Post Office Box 25046, Denver Federal Center, Denver, Colorado 80225
W.N. Mode
Affiliation:
Department of Geology, University of Wisconsin-Oshkosh, Oshkosh, Wisconsin 54901
Meyer Rubin
Affiliation:
United States Geological Survey, National Center, Reston, Virginia 22092
S.W. Robinson
Affiliation:
United States Geological Survey, 345 Middlefield Road, Menlo Park, California 94025
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Abstract

Lake Emma, which no longer exists because of a mining accident, was a tarn in a south-facing cirque near the headwaters of the Animas River in the San Juan Mountains of southwestern Colorado. During the Pinedale glaciation, this area was covered by a large transection glacier centered over the Lake Emma region. Three radiocarbon dates on basal organic sediment from Lake Emma indicate that by ca. 15,000 yr B.P. this glacier, one of the largest in the southern Rocky Mountains, no longer existed. Twenty-two radiocarbon dates on Picea and Abies krummholz fragments in the Lake Emma deposits indicate that from ca. 9600 to 7800 yr B.P., from 6700 to 5600 yr B.P., and at 3100 yr B.P. the krummholz limit was at least 70 m higher than present. These data, in conjunction with Picea:Pinus pollen ratios from both the Lake Emma site and the Hurricane Basin site of J. T. Andrews, P. E. Carrara, F. B. King, and R. Struckenrath (1975, Quaternary Research 5, 173–197) suggest than from ca. 9600 to 3000 yr B.P. timberline in the San Juan Mountains was higher than present. Cooling apparently began ca. 3000 yr B.P. as indicated by decreases in both the percentage of Picea pollen and Picea:Pinus pollen ratios at the Hurricane Basin site (Andrews et al., 1975). Cooling is also suggested by the lack of Picea or Abies fragments younger than 3000 yr B.P. at either the Lake Emma or the Hurricane Basin site.

Type
Research Article
Information
Quaternary Research , Volume 21 , Issue 1 , January 1984 , pp. 42 - 55
Copyright
University of Washington

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References

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