HR: 0800h
AN: PP21A-1547    [Abstracts]
TI: An assessment of the utility of optically-stimulated luminescence to date sediments from Lakes Malawi, Bosumtwi, and Tanganyika, Africa
AU: Gomez, J
EM: jgomez1@uic.ed
AF: University of Illinois-Chicago Dept. of Earth & Environmental SCiences, 845 W. Taylor Street, Chicago, IL 60607-7059 United States
AU: * Forman, S L
EM: slf@uic.edu
AF: University of Illinois-Chicago Dept. of Earth & Environmental SCiences, 845 W. Taylor Street, Chicago, IL 60607-7059 United States
AU: Pierson, J
EM: jpierson@uic.edu
AF: University of Illinois-Chicago Dept. of Earth & Environmental SCiences, 845 W. Taylor Street, Chicago, IL 60607-7059 United States
AU: Scholz, C
EM: cascholz@syr.edu
AF: Dept. of Earth Sciences, Syracuse University, Syracuse, NY 13244-1070 United States
AU: Peck, J
EM: jpeck@uakron.edu
AF: Dept. Geology, Univ. Akron, Akron, OH 44325 United States
AU: Heil, C
EM: CHeil@gso.uri.edu
AF: Grad. School Oceanography, Univ. Rhode Island, Narragansett, RI 02882 United States
AU: King, J
EM: jking@gso.uri.edu
AF: Grad. School Oceanography, Univ. Rhode Island, Narragansett, RI 02882 United States
AU: Shanahan, T
EM: TShanahan@geo.Arizona.EDU
AF: ISPE, Univ. of Arizona, Tucson, AZ 85719-5037 United States
AU: Overpeck, J
EM: JOverpeck@geo.Arizona.EDU
AF: ISPE, Univ. of Arizona, Tucson, AZ 85719-5037 United States
AU: Koeberl, C
EM:
AF: Dept. Geological Sciences, Univ. Vienna Althanstrasse 14, Vienna, A-1090 Austria
AU: Milkereit, B
EM: bm@physics.utoronto.ca
AF: Dept. Physics, Univ. Toronto, Toronto, ON M5S 1A7 Canada
AB: An exciting recent development in geochronology is the advent of optically-stimulated luminescence (OSL) for dating late Quaternary sediments. OSL signal of mineral grains is reset by exposure to sunlight prior to deposition and a time-sensitive charge is acquired from exposure to ionizing radiation post burial. The OSL signal is highly sensitive to solar resetting, with background counts rendered after few minutes of sunlight exposure. OSL geochronology can yield decadal resolution in the past 1000 years, a period of limited precision for radiocarbon dating and potentially date sediment spanning the past 200 to 400 ka. Nearly continuous sedimentary records from African lakes provide unparalleled opportunities to develop new OSL dating approaches to constrain hydro-climatic events in the tropics. A variety of OSL geochronologic approaches are attempted for sediments from Lakes Malawi, Bosumtwi and Tanganyika providing an internal test of reproducibility. Accuracy is assessed by OSL dating levels with radiocarbon ages and with correlated chronologic control e.g. from the sediment magnetic signature or sediment carbon to atmosphere methane relations. The fine-grained (3-11 micron) polymineral and quartz fractions and for coarser levels the quartz fine sand is extracted for dating. Additive and regenerative dose procedures using multiple and single aliquots under blue, green and infrared light exposure are used to estimate the post-burial paleodose. A regenerative procedure with dose normalization and stepped preheating (140-180° C) provides a particularly robust approach for dating sediments greater than 75 ka. OSL emissions for sediment from Lake Malawi for the past ca. 100 ka are not at saturated dose and are amenable for dating by a variety of methods. In contrast sediments from Lake Bosumtwi, with a probable Sahel dust source, exhibit saturation in OSL signal for sediments ca. 100 ka old, necessitating the using of regenerative approaches. The concordance between OSL ages and radiocarbon and correlated chronologic control will be assessed to better define the temporal limits of OSL dating for African lake sediments.
DE: 1105 Quaternary geochronology
DE: 4914 Continental climate records
DE: 4942 Limnology (0458, 1845, 4239)
DE: 9305 Africa
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005