HR: 15:15h
AN: PP53A-06    [Abstracts]
TI: Late Holocene Multiproxy Record (Palynology, Stable Isotope and Multi-Element Geochemistry) of Lake Santa Maria del Oro, Western Mesoamerica.
AU: * Lozano, S
EM: mslozano@servidor.unam.mx
AF: Instituto de Geologia, Universidad Nacional Autónoma de México, Cd. Universitaria. Coyoacán., México, D.F 04510, Mexico
AU: Caballero, M
EM:
AF: Instituto de Geofisica, Universidad Nacional Autónoma de México., Cd. Universitaria. Coyoacán., México, D.F 04510, Mexico
AU: Rodriguez, A
EM: alerdz@geofisica.unam.mx
AF: Instituto de Geofisica, Universidad Nacional Autónoma de México., Cd. Universitaria. Coyoacán., México, D.F 04510, Mexico
AU: Roy, P
EM: pdroy@geofisica.unam.mx
AF: Instituto de Geofisica, Universidad Nacional Autónoma de México., Cd. Universitaria. Coyoacán., México, D.F 04510, Mexico
AU: Sosa, S
EM: susosa@servidor.unam.mx
AF: Instituto de Geologia, Universidad Nacional Autónoma de México, Cd. Universitaria. Coyoacán., México, D.F 04510, Mexico
AB: We present the palynological, stable isotope and major element (ITRAX X-Ray fluorescence) data from a 850-cm sediment sequence from the deepest part of lake Santa María del Oro (SMO) in order to document changes in the climatic and limnological conditions and in the vegetation for the last ca. 5000 yr. SMO is a crater lake of (750 m asl, 2 km diam.) located in a tropical sub-humid climate (1250 mm/yr, average annual temperature 21° C) at the transition between the temperate central Mexican highlands and the arid northern regions. Tropical deciduous forests which loose their leaves for 8 months in a year and the tropical oak forests are the main plant communities in the lake catchments. The western part of Mesoamerica is the cradle of maize (Zea mays ssp. mays ) agriculture; this region is probably one of the two centers of maize domestication based on the presence of one of its closets wild relative teosinte (Zea mays ssp. parviglumis ). Chronology was established with 8 AMS radiocarbon dates. Sediments are finely laminated, with some intervals dominated by black and brown clayey silt and others by brown clayey silt and calcareous silt. In some levels, laminae are characterized by silts and fine sands. Authigenic carbonate laminations are formed during the summer season, when the highest temperatures are reached in the area. Throughout the pollen analysis, teosinte pollen and maize pollen was recorded. The major element concentration (Ca and Ti) in the bulk sediments was analyzed by ITRAX multi-element scanner and the isotopic data (δ¹³C and δ¹⁸O) in authigenic carbonates by mass spectrometer. Ca and Ti ITRAX intensities were calibrated to mass % by using the linear relationship between ITRAX intensity and mass % obtained through conventional XRF analysis. Preliminary pollen data of SMO sediments indicates abundant pollen of teosinte from ca. 2000 to 100 BC and maize presence at ca. 1300 BC and ca. 900 BC along with high charcoal particle concentrations, suggesting early agricultural activity in the area, being the first record of maize in the western region of Mesoamerica. The phases with higher concentration of Ti are identified as periods of higher inflow into the lake basin (BC 1700-1400, 0- AD 200, AD 900 and AD 1800-1900). Phases of higher evaporative conditions are identify at ca. BC 700, BC 400, AD 400-800 and AD 1900-2003 based on Ca high values and enriched δ¹⁸O and δ¹³C. There exists a negative relationship between Ca and Ti. Evidence of changes in climatic conditions is inferred from the data.
DE: 4825 Geochemistry
DE: 4870 Stable isotopes (0454, 1041)
DE: 4942 Limnology (0458, 1845, 4239)
DE: 4950 Paleoecology
DE: 4952 Palynology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly