In this 2005 paper, Rolf Aalto and William Dietrich give a fascinating introduction to their fieldwork on the Strickland River flood plains in Papua New Guinea. This paper focuses on the timing and rate of sediment accumulation in the river. Most of the paper describes the Pb-210 geochronology methods they use to date sediment accumulation. The experiment involves a dating approach this team of scientists have used more than once called CIRCAUS (constant initial river-reach clay activity). This method starts by taking 8-20 measurements of clay-normalized excess Pb-210 activity and many depths in each core .
Aalto and Dietrich use clay normalized pb-210 activity because clay preferentially absorbs mobile Pb-210. They are then able to deduce how much of the pb-210 activity is caused by meteoric rain out and soil radon decay. This allows them to exclusively use mobile pb-210 to measure the rate and timing of sediment accumulation. At the time this paper was written, the two writers had only analyzed 36 of about 200 cores taken from diverse locations in the floodplains. From the 36 cores the analyzed, the authors saw that most of the floodplain has received little to no accumulation over the past 100 years. This is most clearly represented in figure 3, which shows two graphs of DPM/G as a function of Depth (cm) and % Abundance (clay and sand ).
Although one chart is for a terrace well above the floodplain and one is for a core taken from the flood plain, neither shows significant sediment accumulation. In the future, Aalto and Dietrich plan to expand upon their preliminary findings with data from more cores and a better understanding of the way that floods affect their geochronology procedures .