SINGLE-GRAIN OSL DATING OF MISSISSIPPI RIVER TIE CHANNEL DEPOSITS

Aside from historical records (e.g. maps, aerial photos), which are often limited in their coverage and discontinuous in time, there are few viable geochronometric techniques for the study of fluvial processes that have occurred within the last century. Recent equipment advances have made it possible to determine optically stimulated luminescence (OSL) ages from individual sand-size sediment grains and have facilitated the rapid and convenient collection of the quantities of OSL data required for meaningful statistical analysis. Parallel advances in objective analytical methodologies are drastically improving the accuracy of OSL dating, particularly for youthful fluvial sediments. In this investigation we have used single-grain OSL to date sediments deposited by an unaltered tie channel in the lower Mississippi River floodplain approximately 40 miles north of Baton Rouge LA.

Floodplain tie channels link lowland rivers to floodplain lakes, commonly oxbow lakes. This “tie” allows the exchange of water, sediment, nutrients, contaminants and biota between rivers and floodplains. While common throughout the world, documentation of tie channel dynamics and evolution is almost entirely lacking in the geological literature. Single-grain OSL geochronology allowed us to examine the rate of advancement of tie channel deposits into the “Raccourci-Old River” oxbow lake and infer vertical accretion rates along the banks of the channel itself.

This presentation will focus on the experimental and analytical methods utilized, thereby emphasizing the latest advances in OSL dating. All sediments in this study were deposited after A.D. 1850, so the results demonstrate the applicability of single-grain OSL dating to youthful sediments and highlight the potential of the technique to provide temporal constraints for recent sediment transport studies.