HR: 1400h
AN: PP43C-03    [Abstracts]
TI: Preliminary U-Th Dating of Endogenic Gypsum From Lake Petén-Itzá, Guatemala
AU: * Gamble, V C
EM: gamb0039@d.umn.edu
AF: Department of Geological Sciences, University of MN, Duluth, 229 Heller Hall 1114 Kirby Drive, Duluth, MN 55812, United States
AU: Gallup, C D
EM: cgallup@d.umn.edu
AF: Department of Geological Sciences, University of MN, Duluth, 229 Heller Hall 1114 Kirby Drive, Duluth, MN 55812, United States
AU: Hodell, D
EM: dhodell@geology.ufl.edu
AF: Department of Geological Sciences, and Land Use and Environmental Change Institute (LUECI), 441 Williamson Hall, University of Florida, Gainesville, FL 32611, United States
AU: Anselmetti, F
EM: flavio.anselmetti@erdw.ethz.ch
AF: Geological Institute, Swiss Federal Institute of Technology, ETH, Zurich Universtatsstrasse 16, Zurich, 8092, Switzerland
AU: Brenner, M
EM: brenner@ufl.edu
AF: Department of Geological Sciences, and Land Use and Environmental Change Institute (LUECI), 441 Williamson Hall, University of Florida, Gainesville, FL 32611, United States
AU: Ariztegui, D
EM: daniel.ariztegui@terre.unige.ch
AF: Institut Forel, Department of Geology and Paleontology, Université de Genève r. des Maraîchers 13, Geneva, 1205, Switzerland
AB: Uranium-thorium dating of lake sediments can provide accurate ages beyond the range of radiocarbon dating. Many lakes have endogenic precipitation of calcium bearing minerals that allow for substitution by uranium within their crystal structures. The water chemistry of Lake Petén-Itzá, located in northern Guatemala, is dominated by calcium, sulfate and carbonate ions (Deevey et al. 1980; Curtis et al. 1998). Changes in regional climate due to suspected shifts in the ITCZ over the past 85,000 years resulted in both calcite and gypsum deposition, especially during drier periods (Hodell et al. 2006). Both precipitates incorporate uranium from the lake water and can be used for U-Th dating. U-Th dating is problematic in lake systems for several reasons: the potential for 1) diagenetic alteration or dissolution while the endogenic precipitates are settling and after deposition and 2) contamination by detrital thorium. Contamination is a primary issue because of the difficulty of separating the precipitates from the sediment. Despite these concerns, U-Th dating of lake sediments has the potential to be successful with careful selection of precipitates and thorough analysis of the precipitate, the lake system, and the diagenetic environment. Preliminary samples of Lake Petén-Itzá gypsum contain euhedral crystals, indicating a lack of post-depositional alteration. However, the samples have high background thorium levels, indicating the necessity of using the U-Th total sample dissolution isochron dating method (as described by Ku, 2000) to quantify authigenic thorium. Curtis J.H., Brenner M., Hodell D.A., Balser R.A., Islebe G.A., Hooghiemstra H. 1998. A multi-proxy study of Holocene environmental change in the Maya lowlands of Petén, Guatemala. Journal of Paleolimnology 19, 139-159. Deevey E.S., Brenner M., Flannery M.S., Yezdani G.H. 1980. Lakes Yaxha and Scanab, Petén, Guatemala: Limnology and hydrology. Arch. Hydrobiol. 57, 419-460. Hodell D.A., Anselmetti F.S., Brenner M., Ariztegui D. 2006. The Lake Petén-Itzá Scientific Drilling Project. Scientific Drilling 3, 25-29. Ku T-L. 2000. Uranium series methods: in Quaternary Geology: Methods and Applications. AGU Reference Shelf 4, 101-114.
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
DE: 9345 Large bodies of water (e.g., lakes and inland seas) (0746)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly