Erwin, Diane , Myers, Jeffrey A. , Schorn, Howard E. .
Are there Neogene "lowland" floras preserved near the modern-day crest of the central Sierra Nevada, CA?
In light of ongoing debate about the uplift history of the Sierra Nevada, a question remains concerning whether or not several Neogene floras preserved near today's crest represent "lowland" forests that grew at <915 m (3000 ft.) elevation. The Mt. Reba and Elephants Back (EB) assemblages sit above treeline at >2637m (8650 ft.) leaving one to indeed wonder about the landscape and climate in which they grew. As currently described, the Mt. Reba includes cypress (Cupressus), Douglas fir (Pseudotsuga), two evergreen oaks (Quercus, Lithocarpus), two pines (Pinus), fir (Abies), giant sequoia (Sequoiadendron), and juniper (Juniperus). Using the "similar living species" method paleoelevation estimates were between ~762 to 915 m (~2500 - 3000 ft.) suggesting a post-7 Ma uplift of ~1829 m (6000 ft.). Similarly, the Lower (~16 Ma?) and Upper EB (~7 Ma) floras described as mixed broad-leaved evergreen and deciduous hardwood forest with no conifers implied growth at ~762 to 915 m (~2500 - 3000 ft.) elevation. From our floristic analysis of the Mt. Reba plants we estimate a MAT of 8-9°C (not 13.3°C) and elevation of at least 1524m (5000 ft.), if not higher, given the relatively warmer and wetter late Miocene climate. With respect to the EB floras, the age and stratigraphic position of the Lower assemblage, in particular, is problematic. The Upper EB has three taxa: Lyonothamnus, Nerium, and several cf. Quercus alba-type leaves. Only the oak is identifiable to genus. The Lower EB includes deciduous hardwoods (e.g., Populus, Salix, Juglans, Ulmus, Quercus, Platanus) and evergreen shrubs that are not exclusively low elevation taxa, but conifers are absent. If the Lower EB flora is ~16 Ma based on new geologic mapping and radioisotopic dates, floral analysis must take into account growth during the Mid-Miocene Climatic Optimum, a time of elevated global temperatures, increased precipitation and humidity that would allow forest growth at elevations >915 m (3000 ft.).
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1 - University of California, Museum of Paleontology, 1101 Valley Life Sciences Building, Berkeley, CA, 94720, USA
2 - Western Oregon University, Department of Geology, Monmouth, OR, 97361, USA
3 - 337 Mari Court, Ridgecrest, CA, 93555, USA
Mt. Reba paleoflora
Elephants Back paleofloras
Presentation Type: Oral Paper:Papers for Sections
Location: Forsyth Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 2:30 PM