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.
Bibliographical notePublisher Copyright:
© 2014 University of Washington.
Copyright 2015 Elsevier B.V., All rights reserved.
- Bull Lake glaciation
- Pleistocene fossils
Continental Scientific Drilling Facility tags