HR: 0800h
AN: PP21A-1546    [Abstracts]
TI: Sediment Magnetic Hysteresis Measurements as a Paleoclimate Proxy From Lake Bosumtwi, Ghana
AU: * Fox, P A
EM: paf2@uakron.edu
AF: Department of Geology, The University of Akron, Akron, OH 44325-4101 United States
AU: Peck, J A
PP21A-1546 AF: Department of Geology, The University of Akron, Akron, OH 44325-4101 United States
AU: Shanahan, T
PP21A-1546 AF: Dept. of Geological Sciences, The University of Arizona, Tucson, AZ 85721 United States
AU: King, J W
PP21A-1546 AF: Grad. School of Oceanography, The University of Rhode Island, Narragansett, RI 02882 United States
AU: Scholz, C A
PP21A-1546 AF: Dept. Earth Sci., Syracuse University, Syracuse, NY 13244-1070 United States
AU: Overpeck, J T
PP21A-1546 AF: Dept. of Geological Sciences, The University of Arizona, Tucson, AZ 85721 United States
AU: Amoako, P Y
PP21A-1546 AF: Ghana Geological Survey Department, Ministry Branch Post Office, Accra, M80 Ghana
AB: Lake Bosumtwi occupies a 1.07 Ma impact crater in the West African country of Ghana. The hydrologic closure and extremely small drainage basin makes for a strong correlation between lake level and the regional moisture balance. Lake drilling in the crater's annular moat recovered the complete sediment record (294 m) spanning the one million year history of the crater. These drill cores were sampled for magnetic hysteresis measurements at a 1 m (about 3 to 4 ka) interval. Magnetic hysteresis properties provide a measure of the magnetic concentration, magnetic grain size, and magnetic mineralogy in the sediment and have been successfully used as a paleoclimate proxy in a wide variety of depositional environments. Fluctuating environmental conditions change components of depositional systems such as sediment sources and transport pathways. These components, in turn, influence the type of sediment accumulating and therefore the magnetic properties of the sediment. The most recent interglacial and glacial periods have been well dated in Lake Bosumtwi sediments. The present interglacial period is characterized by S ratios greater than 0.8 and Hcr values less than 50 mT. This low coercivity magnetic mineral assemblage accumulated during the wet interglacial period. This time includes the moist North African Humid Period in the Holocene when Lake Bosumtwi overflowed the surrounding crater wall. The glacial-age sediment contains high coercivity minerals indicated by S ratios less then 0.7 and Hcr values between 60 and 80 mT. The increase in high coercivity minerals likely results from increased aeolian dust flux from arid Sahel sources at a time of greatly weakened summer monsoons. Applying these two magnetic mineral assemblages deeper down, beyond the dated portion of the core, allows interglacial/glacial cycles to be identified back to approximately 400 ka. Work is currently in progress to finish hysteresis measurements in the lower half of the drill core thereby extending the rock magnetic climate proxy record to 1 Ma.
DE: 1527 Paleomagnetism applied to geologic processes
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4942 Limnology (0458, 1845, 4239)
DE: 9305 Africa
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005