HR: 0800h
AN: U21A-0701    [Abstracts]
TI: The Lake Tanganyika Accommodation Zone Structural Highs: Probable Archive of Continuous Miocene to Recent Paleoenvironmental and Paleoclimatic Information for East Africa
AU: Cohen, A S
EM: acohen@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, Dept. of Geosciences University of Arizona Gould Simpson Bldg #77, Tucson, AZ 85721 United States
AU: * Lezzar, K E
EM: klezzar@hotmail.com
AF: Department of Geosciences, University of Arizona, Dept. of Geosciences University of Arizona Gould Simpson Bldg #77, Tucson, AZ 85721 United States
AU: Russell, J
EM: russ0154@UMN.EDU
AF: Limnological Research Center, University of Minnesota, Limnological Research Center University of Minnesota, Minneapolis, MN 55455 United States
AU: Scholz, C A
EM: cascholz@syr.edu
AF: Department of Earth Sciences, Syracuse University, Department of Earth Sciences, 208 Heroy Geology Laboratory Syracuse University, Syracuse, NY 13244 United States
AU: Tiercelin, J
EM: jjtierc@univ-brest.fr
AF: Inst. Universitaire Euro. de la Mer, Inst. Universitaire Euro. de la Mer Place N. Copernic, Plouzane, 29280 France
AU: Gans, C R
EM: cgans@geodyn.psu.edu
AF: Department of Earth Sciences, Syracuse University, Department of Earth Sciences, 208 Heroy Geology Laboratory Syracuse University, Syracuse, NY 13244 United States
AU: Helfrich, L C
EM: elcody@email.arizona.edu
AF: Department of Geosciences, University of Arizona, Dept. of Geosciences University of Arizona Gould Simpson Bldg #77, Tucson, AZ 85721 United States
AB: Continental drilling of lake deposits has proven an important source of high-resolution paleoclimatic and paleoenvironmental information. The large rift lakes of East Africa react dramatically to climatic perturbations, recording responses in sedimentary records of lake level, chemistry, and biota. No continuous continental paleoclimate records covering the full period of hominid evolution, especially the critical transitions of the late Miocene through the Plio-Pleistocene, are currently available or forthcoming. However, approximately 1000 km of sparker and air gun reflection seismic profiles collected during a number of field campaigns on Lake Tanganyika demonstrate the existence of three major mid-lake isolated structural highs: from N-S the Ubwari, Kavala Island, and Kalya horsts, whose sedimentary cover may provide records of this critical interval. Several coring campaigns demonstrated sedimentation rates over the last 100 ka much slower than adjacent basinal settings, in some cases as low as 0.1 mm/year. Sequence stratigraphic analyses of sediments on the shallower (300-500 m) of these horsts (Ubwari and Kavala Island), and on other structural platforms have shown the presence of numerous unconformities related to lake level fluctuations and paleoclimatic variability. During the Last Glacial Maximum, for example, features such as prograding delta lobes and paleochannels indicate water levels may have fallen by as much as 360 meters. Erosional unconformities at depths of as much as 600 m have been noted at basinal sites adjacent to these relatively shallow horsts. The northeastern edge of the Kalya horst, however, lies at sufficient water depths ($>$ 600 m) to have escaped these major erosional truncations. Furthermore, this site is located in a depositional environment of relative tectonic quiescence, apparently undisturbed by faulting, unlike the northern structural highs. Preliminary seismic stratigraphic analysis of the Kalya horst shows the presence of at least 300 m of continuously accumulated sediment. Cores from the region, spanning the late Pleistocene and Holocene, have shown that the sediments are partially laminated and contain a wealth of geochemical and paleoecological indicators of glacial-interglacial to millennial-scale hydroclimatic fluctuations. Given the age of Lake Tanganyika (10-12 Ma) and the highly continuous nature of sedimentation on the deep accommodation zone, the Kalya horst has the potential to provide a continuous and readily-interpretable record of paleoclimate history over much, if not all, of the critical phases of hominid evolution in East Africa.
DE: 9305 Africa
DE: 9604 Cenozoic
DE: 3344 Paleoclimatology
DE: 4239 Limnology
DE: 1845 Limnology
SC: Union [U]
MN: 2004 AGU Fall Meeting