2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 302-9
Presentation Time: 11:00 AM


CLARK, Nichole1, BROOKS, Gregg1, LARSON, Rebekka1 and HOLMES, Charles2, (1)Marine Science, Eckerd College, 4200 54th Avenue South, St. Petersburg, FL 33711, (2)Environchron, 9103 64th Ave East, Bradenton, FL 34202

Americium-241 (241Am) and Cesium-137 (137Cs) are short-lived radioisotopes with half-lives of ~432 and ~30 years, respectively. Both are thermonuclear by-products, and therefore can be used as stratigraphic markers for the peak of nuclear weapons testing in the early to mid 1960s. Both 241Am and 137Cs easily adhere to fine-grained sediments, but 137Cs is utilized more often because of its high detectability using gamma spectroscopy. However, 137Cs tends to be more susceptible to migration in organic-rich sediments, which can restrict its geochronologic use in these types of environments. Americium-241 is less mobile, thus having the potential to be more applicable in peaty, organic-rich settings. This study utilizes 241Am in collaboration with 137Cs, to validate Lead-210 (210Pb) age-dates in sediment cores from a variety of natural and anthropogenically impacted environments throughout the U.S. Virgin Islands. A positive relationship was found between 241Am and 137Cs profiles in some of the cores analyzed. After applying the CRS model to the 210Pb profiles, which gave the dates for each data point, it was determined that the peaks agree well with an early 1960s date. In many cases the 241Am peak was more well defined than the 137Cs peak. This suggests that 241Am can be used as a replacement, or paired with 137Cs, in organic-rich sediments to validate the height of nuclear weapons testing in the early to mid 1960s, and/or potentially other nuclear disasters (e.g. Chernobyl, 1986).