HR: 0800h
AN: PP21A-1553    [Abstracts]
TI: Geochemical and Sedimentological Records of Late Quaternary Climate Change, Lake Tanganyika, Tropical East Africa
AU: * Felton, A A
EM: afelton@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building, 1040 E. 4th St., Tucson, AZ 85721
AU: Russell, J M
EM: russ0154@umn.edu
AF: Department of Geological Sciences, Brown University, BOX 1846, Providence, RI 02912
AU: Cohen, A S
EM: acohen@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building, 1040 E. 4th St., Tucson, AZ 85721
AU: Baker, M E
EM: mbaker@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building, 1040 E. 4th St., Tucson, AZ 85721
AU: McGlue, M M
EM: mmcglue@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building, 1040 E. 4th St., Tucson, AZ 85721
AU: Lezzar, K E
EM: klezzar@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building, 1040 E. 4th St., Tucson, AZ 85721
AB: We have analyzed piston core records from Lake Tanganyika (western Tanzania, East African Rift Valley) to investigate possible signals of tropical paleoclimate change during the Late Quaternary. Long paleoclimate records from East Africa are of importance for understanding climatic processes such as the role of solar variability in regulating tropical climates at Milankovitch time scales, and the relationship between abrupt climate changes, migration of Intertropical Convergence Zone, and regional climate variability (Nicholson, 2000). However, records of pre-Holocene climate variability from tropical African lakes (>25ka) are still quite rare. Long records from Lake Tanganyika are of particular interest given the lake's antiquity and its demonstrated potential for producing high resolution (frequently annually laminated) sedimentary records (Cohen et al., 1993). We analyzed physical properties, grain size, total organic carbon, major, minor and trace element variability, and biogenic silica data for a 7.75 m core from the Kalya slope and horst region of central Lake Tanganyika at 640m water depth. Nine 14C dates provide an age model for the core, which spans ~62 cal kyr. Elemental concentrations preserved in Lake Tanganyika sediments record variability in deposition and runoff into the lake basin. Under conditions of rapid erosion, exposure and rapid weathering of bedrock has been shown to generate high concentrations of original silicate minerals enriched in soluble cations such as sodium and potassium, elements that are also biologically conservative. Prior to 40ka cal yr. core sediments are characterized by high magnetic susceptibility, intermediate levels of organic carbon, low to intermediate levels of biogenic silica, and fine grain size, indicative of relatively high precipitation. There is a profound decrease in magnetic susceptibility, a decrease in organic carbon and an increase in grain size at 40ka cal yr, which persists until ~16ka cal yr. Seismic reflection profiles demonstrate the existence of paleodeltas at ~360m below modern lake level that may have formed during this period, although it is unclear whether this deposit represents a Late Quaternary (OIS 2) or earlier (OIS 6) event. Maximum aridity occurred at about 20-20.5ka cal yr, consist with earlier interpretations of lake lowstands (Gasse et al., 1989, Scholz et al., 1997). The late Pleistocene and earliest Holocene sediments in our record are characterized by generally rising magnetic susceptibility, declining organic carbon and biogenic silica, and finer grain size. However during this period there are marked fluctuations in magnetic susceptibility and biogenic silica at millennial time-scales. These indicate intervals of fluctuating precipitation, productivity, and possibly windiness and are particularly prominent during the Pleistocene-Holocene transition. Massive clays, rising magnetic susceptibility, low biogenic silica and low organic carbon mark the early Holocene, indicative of increased rainfall during a regionally wet interval. These sediments are capped by a laminated ooze, indicative of drier conditions and a more stratified water body.
DE: 1051 Sedimentary geochemistry
DE: 1065 Major and trace element geochemistry
DE: 9305 Africa
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005