Tie channel sedimentation rates, oxbow formation age and channel migration rate from optically stimulated luminescence (OSL) analysis of floodplain deposits

Using optically stimulated luminescence (OSL) analysis we obtained depositional ages ranging from 25 10 to 928 144 years before present for sediments deposited in oxbow lakes along three lowland river systems. The dated sediments were collected from the banks of tie channels along the Lower Mississippi River, the Fly River in Papua New Guinea, and Birch Creek along the Yukon River in Alaska. Tie channels connect the oxbow lakes to the main stem river and allow the exchange of water and suspended sediment between the two. The banks consist of fine sand and sandy silt beds interlayered with silt and clay. OSL samples were collected both horizontally from exposed banks and vertically by coring through levee crests; sample collection was targeted at beds containing appreciable quantities of fine sand. OSL ages were determined using single-grain or in some cases single-aliquot techniques and dose distribution analysis. Samples were first collected along the Lower Mississippi tie channel to compare OSL dates with historical data sources and test the applicability of OSL in these settings; the OSL dates agreed closely with historical data. In all three river systems, OSL dating allowed the determination of vertical accretion rates, tie channel advancement rates, and oxbow lake ages. In Papua New Guinea, OSL sampling also provides an estimate of lateral migration rates of the Fly River and allows a comparison of modern mine-influenced deposition rates with natural background rates over the last 1000 years. Results from Papua New Guinea and the Mississippi River suggest that the advancement rate of tie channels responds directly to changes in the sediment load of the main stem river. Copyright (c) 2005 John Wiley & Sons, Ltd.