HR: 14:55h
AN: H23J-06    [Abstracts]
TI: A Discordancy Between Short-Term Sedimentation Rate Using Pb-210, Cs-137 and Pu and Long-Term Sedimentation Rate Using C-14
AU: * Baskaran, M
EM: Baskaran@wayne.edu
AF: Wayne State University, Department of Geology, Detroit, MI 48202 United States
AU: Filley, T R
EM: filley@purdue.edu
AF: Purdue University, Department of Earth and Atmospheric Sciences, West Lafayette, IN 47907 United States
AU: Bianchi, T S
EM: tbianch@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AU: Freeman, K H
EM: kate@essc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, University Park, PA 16802 United States
AU: Hatcher, P G
EM: hatcher@chemistry.ohio-state.edu
AF: Ohio State University, Department of Chemistry, Columbus, OH 43210 United States
AB: Short-lived radionuclides (²¹⁰Pb, ¹³⁷Cs, etc) have been successfully utilized to obtain sedimentation rates in freshwater and coastal marine environments over the past 3 decades. Combined use of ²¹⁰Pb and Pu enable to delineate sedimentation from sediment mixing. However independent validation of short-term accumulation rates using other long-lived isotopes, such as ¹⁴C are very limited. We collected a sediment core from a sinkhole lake, Mud Lake, Florida, USA and analyzed it for ²¹⁰Pb, ¹³⁷Cs, ^239,240Pu and ¹⁴C. The sediment inventories of ¹³⁷Cs, and ^239,240Pu are comparable to the regional global fallout values while ²¹⁰Pb inventory is comparable to the value reported for this region. A plot of depth against ¹⁴C age yields an intercept value of 1070 yrs, indicating a reservoir correction age of 1070 yrs. Most of the data points fall either on the straight line or close to the line possibly suggesting that the relative proportion of fossil carbon had remained constant throughout the core. Due to sediment compaction, a comparison of linear sedimentation rate obtained using short-lived radionuclides with those ¹⁴C could yield considerable difference and hence we compared the mass accumulation rates obtained from these isotopes. The ²¹⁰Pb_xs-based sediment mass accumulation rate of 17 mg cm^-2 y^-1, is almost a factor of 3 higher than that obtained using ¹⁴C -derived mass accumulation rate of 6 mg cm^-2 y^-1. The peak fallout of Pu is well preserved in the lake core suggesting relatively minimum sediment mixing. The factors that could cause this discordancy between the long-term and short-term mass accumulation rates will be discussed.
DE: 1115 Radioisotope geochronology
DE: 1120 Isotopic disequilibrium dating
DE: 1165 Sedimentary geochronology
DE: 1861 Sedimentation (4863)
SC: Hydrology [H]
MN: Fall Meeting 2005