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Geologic setting and stratigraphy of the Ziegler Reservoir fossil site, Snowmass Village, Colorado

Published online by Cambridge University Press:  20 January 2017

Jeffrey S. Pigati ,
Ian M. Miller ,
Kirk R. Johnson ,
Jeffrey S. Honke ,
Paul E. Carrara ,
Daniel R. Muhs ,
Gary Skipp  and
Bruce Bryant
Jeffrey S. Pigati*
Affiliation:
U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225, USA
Ian M. Miller
Affiliation:
Department of Earth Sciences, Denver Museum of Nature and Science, Denver, CO 80205, USA
Kirk R. Johnson
Affiliation:
Department of Earth Sciences, Denver Museum of Nature and Science, Denver, CO 80205, USA
Jeffrey S. Honke
Affiliation:
U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225, USA
Paul E. Carrara
Affiliation:
U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225, USA
Daniel R. Muhs
Affiliation:
U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225, USA
Gary Skipp
Affiliation:
U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225, USA
Bruce Bryant
Affiliation:
U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225, USA
*
⁎Corresponding author. Tel.: + 1 303 236 7870 (phone); fax: + 1 303 236 5349.E-mail address:jpigati@usgs.gov (J.S. Pigati).
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Abstract

The geologic setting of the Ziegler Reservoir fossil site is somewhat unusual — the sediments containing the Pleistocene fossils were deposited in a lake on top of a ridge. The lake basin was formed near Snowmass Village, Colorado (USA) when a glacier flowing down Snowmass Creek Valley became thick enough to overtop a low point in the eastern valley wall and entered the head of Brush Creek Valley. When the glacier retreated at about 155–130 ka, near the end of Marine Oxygen Isotope Stage 6, the Brush Creek Valley lobe left behind a moraine that impounded a small alpine lake. The lake was initially ~ 10 m deep and appears to have been highly productive during most of its existence, based on the abundant and exquisitely preserved organic material present in the sediments. Over time, the basin slowly filled with (mostly) eolian sediment such that by ~ 87 ka it contained a marsh or wetland rather than a true lake. Open-water conditions returned briefly between ~ 77 and 55 ka before the impoundment was finally breached to the east, establishing ties with the Brush Creek drainage system and creating an alpine meadow that persisted until historic times.

Keywords

Bull Lake glaciationPleistocene fossilsSnowmastodonPaleoclimateStratigraphy
Type
Articles
Information
Quaternary Research , Volume 82 , Issue 3 , November 2014 , pp. 477 - 489
Copyright
University of Washington

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Footnotes

1 Current address: National Museum of Natural History, Smithsonian Institution, 1000 Jefferson Dr SW, Washington, DC 20004, USA.

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