Extent, timing, and climatic significance of latest Pleistocene and Holocene glaciation in the Sierra Nevada, California
- Univ. of Washington, Seattle, WA (United States)
Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relative weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before ~13,100 cal yr B.P.. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic 10Be and 26Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.
- Research Organization:
- Washington Univ., Seattle, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC05-76OR00033
- OSTI ID:
- 527434
- Report Number(s):
- DOE/OR/00033-T709; ON: DE97053336; TRN: AHC29720%%26
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1995
- Country of Publication:
- United States
- Language:
- English
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