2007 GSA Denver Annual Meeting (2831 October 2007)
Paper No. 123-4
Presentation Time: 8:45 AM-9:00 AM


KOUWENBERG, Lenny1, BROUGHTON, Julie2, TIFFNEY, Bruce2, and MCELWAIN, Jennifer3, (1) Integrative Biology, University of california, Berkeley, 3060 Valley Life Science Building, Berkeley, CA 94720, lenny.kouwenberg@berkeley.edu, (2) Department of Earth Science, University of California, Santa Barbara, CA 93106, (3) Department of Biological and Environmental Science, University College Dublin, Bellfield, Dublin 4, Dublin, D4, Ireland

The topographic history of the Sierra Nevada has been the focus of an increasing number of studies, but because of conflicting results derived from different methods, the actual altitudinal history remains unresolved. Quantitative paleoelevation studies based on oxygen and hydrogen isotopes, thermochronology and paleobotanical proxies argue that the Sierra Nevada were high-standing during the early Cenozoic and may have lost elevation since. In contrast, river incision and stratigraphic tilt studies claim that the main elevation gain was not obtained until the Pliocene, associated with the delamination of an eclogite root under the southern Sierra Nevada. In order to resolve the current discrepancies in the topographic development of the northern Sierra Nevada, we have estimated the paleoelevation of two early-middle Miocene sites in the northern Sierra Nevada, using a new paleobotanical proxy based on the response in stomatal density on leaves to decreasing CO2 partial pressure with altitude.

Stomatal analysis of fossil Quercus pseudolyrata leaves indicates a paleoelevation for Gold Lake of 2152 519 m, 139 m higher than present, and for Mohawk of 2051 286 m, 665 m higher than present. The uncertainty in coeval sea-level CO2 estimations provides the largest source of potential error in this novel method. The lowest estimated elevations, using the maximum likely CO2 concentration, were at least 1500 m a.s.l. during the early-middle Miocene for both sites. Paleoelevation estimates using established paleobotanical methods (Leaf Margin Analysis, CLAMP and the Nearest Living Relative method) for the Gold Lake and Mohawk floras are remarkably consistent with stomata-based estimates. The paleobotanical data reported here from the Mohawk and Gold Lake floras indicate that a previously suggested post-Eocene uplift of ~500 m had already been gained by the Miocene, strongly arguing against a significant Pliocene uplift phase linked to mantle delamination under the northern Sierra Nevada, without unprecedented Late Miocene erosion to remove previously established relief.

2007 GSA Denver Annual Meeting (2831 October 2007)
General Information for this Meeting
Session No. 123
Tectonics; Neotectonics/Paleoseismology I
Colorado Convention Center: 403
8:00 AM-12:00 PM, Tuesday, 30 October 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 339

© Copyright 2007 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.