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Abstract Detail


Paleobotanical Section

Broughton, Julie [1], McElwain, Jennifer [2], Kouwenberg, Lenny [2], Tiffney, Bruce [3].

The Mohawk Valley Flora: Paleoclimate, paleoecology and the testing of a new paleoaltitude method from the Miocene of the northern Sierra Nevada, CA.

THE Mohawk Valley Regional Flora (Gold Lake Flora and Mohawk Flora) fills a gap in the Miocene floral history of the northern Sierra Nevada, and possesses the preservational quality required for testing a novel method of estimating paleoelevation. Calculating paleoelevation has long been a challenge in understanding mountain uplift; geologists can infer the existence of a mountain range, but assessing paleohypsometry and paleorelief is far more difficult. Various geological methods have been employed to quantify the elevational history and paleoaltitude (oxygen isotope data, basaltic vesicularity) in conjunction with paleobotanical methods (CLAMP, Leaf Margin Analysis) suggesting the Sierra Nevada was a topographic feature as early as 20 Ma and may have experienced a loss of elevation. The use of stomatal density as a proxy for CO2 partial pressure is a new method independent of ecological or local climatic variability. Initial analysis of the Mohawk Valley Flora suggests paleoelevation of 2243 m at Gold Lake (present elevation 2013 m) and 2142 m at Mohawk (present elevation 1386 m) indicating a paleoelevation near present-day if not an elevation loss of between 250 and 900m over the last 18 million years.
In addition to the use for paleoelevation, the Mohawk Valley Flora has also yielded the first clear reports of Zanthoxylum, Staphylea, Oxalis, Cercidiphyllum and a tentative report of Stratioites within the Miocene of western North America. Incorporation of these and other taxa allow for climatic interpretation through the use of Leaf Margin Analysis and a modified Nearest Living Relative method. Preliminary results indicate the Mohawk Valley Flora may represent an upland tongue of mixed mesophytic vegetation existing near the end of the Miocene Climatic Optimum.


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1 - University of California, Earth Science, Santa Barbara, California, 93106, USA
2 - Field Museum of Natural History, Department of Geology, 1400 South Lake Shore Drive, Chicago, Illinois, 60605, USA
3 - University of California Santa Barbara, Geological Sciences, Santa Barbara, California, 93106, USA

Keywords:
Miocene
Mohawk Valley Flora
Sierra Nevada
Tertiary
Paleoaltitude
CO2 partial pressure.

Presentation Type: Oral Paper:Papers for Sections
Session: 17-14
Location: 266/Holt
Date: Monday, July 31st, 2006
Time: 4:45 PM
Abstract ID:259


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