Storm deposition and 137Cs accumulation in fine-grained marsh sediments of the Mississippi Delta plain

Cesium-137 activity and ash contents were measured in shallow cores from marshes on a salinity gradient in the Mississippi Delta plain. Average accretion rates calculated from 137Cs activity profiles are similar to those previously reported. Our study, however, demonstrates anomalies associated with storm deposits which may help in interpretation of activity profiles in other regions. We also find trends in activity profiles related to the salinity gradient which had not previously been described in subaerial sediments. Our results suggest that there is a major difference between 137Cs accumulation patterns in systems restricted to relatively fine-grained sediments and those with coarse-grained sediments. To understand and properly interpret patterns of 137Cs activity for sedimentary accretion rates in such systems it is imperative that relative concentrations of clastic material determined and storm deposits be recognized. (Author)