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Limitations of absolute age constraints for the Quaternary morainal record in the Eastern Sierra Nevada, California from detailed stratigraphic relationships of the Casa Diablo till Margie B. DeRose Martin J. Kennedy Department of Earth Sciences University of California, Riverside High Resolution Climate Records North Atlantic δ18O Records Marine sediment cores Greenland ice cores North Atlantic Marine Sediment WARM COLD Raymo (1994) 3 Million-year δ18O record Greenland Ice 1 • +120 ka δ18O record COLD Å WARM Æ Steffensen, et al. (2008) Greenland Ice Core WARM COLD Altabet, et al. (2002) Rapid Changes GISP2 Alley, et al. 1993 WARM ↑ COLD ↓ Sierra Nevada N rra Sie a ad ev http://geon.unavco.org/unavco/lib/images/California_3D_Relief_topography_oblique.jpg ra er Si v Ne a ad http://www.goes-arch.noaa.gov/cgi-bin/post-archive North Atlantic & Greenland ice records • Relevance to the Sierran climate record? North Atlantic & Greenland ice records • Relevance to the Sierran climate record? • Frequency of abrupt change recorded in the Sierra? North Atlantic & Greenland ice records • Relevance to the Sierran climate record? • Frequency of abrupt change recorded in the Sierra? • Cyclicity and timing of events? North Atlantic & Greenland ice records • Relevance to the Sierran climate record? • Frequency of abrupt change recorded in the Sierra? • Cyclicity and timing of events? • In phase with the North Atlantic records? North Atlantic & Greenland ice records • Relevance to the Sierran climate record? • Frequency of abrupt change recorded in the Sierra? • Cyclicity and timing of events? • In phase with the North Atlantic records? • Stable or unstable? Å WARM COLD Æ Santa Barbara Basin ODP Site 893 (Robert, 2004) Death Valley (Yang, et al., 2005) Mono Lake (Benson et al., 1998) ra er Si Mono Lake da va Ne Death Valley Santa Barbara Basin ODP 893 http://fermi.jhuapl. edu/states/maps_ bw/ca_bw.gif Sierran Climate Record • Frequency of ice advance in Sierra – Connection with Northern Hemisphere climate • Moraines – Direct record of glacial advance & retreat Convict Lake • Photo of Convict Lake & recessional moraines (Google™ Earth Image, 2008) Pine Creek (Google™ Earth Image, 2008) Sierran Climate Record • Chronology for morainal record – timing, magnitude, & frequency • Age control – 14C • Limited to ~40,000 yr and younger (Walker, 2005) – Cosmogenic • Potential error of at least 20% (Walker, 2005) • Need absolute age control Mammoth Lakes www.mapquest.com Glacial Geologic Map of the Long Valley Caldera (Bailey, 1989) Volcanic Geologic Map of the Long Valley Caldera (Bailey, 1989) Absolute Age Constraints • Stratigraphic Relationships • Only 2 absolute age constraints – Sherwin till – Casa Diablo till • Chronology of Sierran glacial record Sherwin Till Bishop Tuff 759 ± 2ka 40K/40Ar (Sarna-Wojcicki et al., 2000) Bishop Tuff Sherwin Till HWY 395 Casa Diablo Till Casa Diablo Till Map: Bailey (1989) miles Casa Diablo Till Lower Basalt 126 ± 25 ka Map: Bailey (1989) 40K/40Ar miles (Bailey, 1976) Casa Diablo Till Upper Basalt 62 ± 13 ka 40K/40Ar (Bailey, 1976) Map: Bailey (1989) miles Detailed Mapping Casa Diablo till • Address bounding age relationships • Show relative ages • Relation to volcanics • Any new relationships Preliminary Results • Lack of evidence for the upper bounding basalt flow – No younger age control • New undocumented relationships – Potential additional age constraints • Improve resolution of the Sierran climate record Conclusions • Void in established chronology for the Sierran glacial record • Correlation with broader records • Additional age controls may exist • Clear need for further detailed studies • Improve chronology • Hemispheric teleconnections Project Support • Valentine Eastern Sierra Reserve Graduate Student Research Grant 2008 • White Mountain Research Station Graduate Student Minigrant 2008 • John Dunham Field Fellowship, Department of Earth Sciences, University of California, Riverside 2008