HR: 0830h
AN: OS11A-21    [Abstracts]
TI: In the Land of the Sky: Recent Paleoenvironmental Research From Coastal Oaxaca, Mexico
AU: * Goman, M F
EM: mg254@cornell.edu
AF: Michelle Goman, Dept. of Earth and Atmospheric Sciences Cornell University, Ithaca, NY 14853 United States
AU: Joyce, A A
EM: Arthur.Joyce@Colorado.edu
AF: Arthur Joyce, Dept. of Anthropology, University of Colorado,, Boulder, CO 80309 United States
AU: Mueller, R G
EM: Raymond.Mueller@stockton.edu
AF: Raymond Mueller, Dept. of Environmental Studies, Richard Stockton College of New Jersey, Pomona, NY 08240 United States
AB: The Lower Río Verde Valley of Oaxaca has had a long and complex cultural history in part shaped by significant landscape change that ocurred 2300 years ago, when the Río Verde river changed morphology from a meandering to a braided form. These changes were precipitated by anthropogenic landuse impacts in the highland valleys of Oaxaca over 125 linear km to the north. While the lower valley's geomorphic history is well studied, little is known of its paleoecology. In order to reconstruct the history of vegetation, climate, and associated land use change, sediment cores were raised from several sites throughout the region. We present stratigraphical, palynological, and charcoal data from three sites in the region. The lower drainage basin consists entirely of the Verde's coastal valley. The climate of the lower Río Verde Valley is hot and humid with mean annual rainfall of 1000 mm to 2000 mm and average temperatures range from 25°C to 28°C. We discuss the pollen and stratigraphic record from Laguna Pastoría which is a brackish estuary protected from the Pacific Ocean by a roughly east-west trending bay barrier. The bay barrier is about 500 m wide and 2 to 4 m high. Low scrub vegetation (cacti, thorny bushes, small trees and palms) grow on the barrier. The lagoon itself is approximately 9 km long and varies in depth with a 3-4 m maximum. Tides are microtidal (1 m). The lagoon supports a diverse array of mangroves (Rhizophora mangle, Laguncularia racemosa, Conocarpus erectus and Avicennia germinans). Two sediment cores were raised from the lagoon (LP1 and LP2) and provide a record of hurricane strikes and possible changes in the frequency of El Niño's. The LP1 core covers approximately the last 5000 yrs. Preliminary pollen analysis indicates that pollen is in excellent condition and is diverse (>60 taxa). Zea mays pollen was identified from sediments dating to the early Formative period (~ 3600 yr ago). The charcoal records analyzed from 2 paleomeanders of the Río Verde are also discussed. The sediments from these sites are dominated by clays and have a low organic content, pollen preservation was poor. However, microscopic and macroscopic charcoal are well preserved. These data provide a long term record of changing fire history for the region as far back as the late Archaic Period.
DE: 1620 Climate dynamics (3309)
DE: 4215 Climate and interannual variability (3309)
DE: 4239 Limnology
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly