. Bulletins of American paleontology. 12 3 4 5 6 Total Activity - dpm/g (Radium-226 and Lead-210) Text-figure 3.—Distribution of --''Ra and total -'"Pb in the Russell Bank (Core 19C). 20 40 i 60 Q 80 100 120 140. 12 3 4 5 6 Total Activity (dpm/g) Text-figure 4.—Distribution of --"Ra and total '"'Pb in the Whi- pray Basin Core 5G. Also plotted is the total -'"Pb as determined by gamma spectroscopy that demonstrates very good agreement be- tween the two methods. However, for non-accreting banks, where -'"Pb activity approaches a minimum in the upper part of the cores, th
. Bulletins of American paleontology. 12 3 4 5 6 Total Activity - dpm/g (Radium-226 and Lead-210) Text-figure 3.—Distribution of --''Ra and total -'"Pb in the Russell Bank (Core 19C). 20 40 i 60 Q 80 100 120 140. 12 3 4 5 6 Total Activity (dpm/g) Text-figure 4.—Distribution of --"Ra and total '"'Pb in the Whi- pray Basin Core 5G. Also plotted is the total -'"Pb as determined by gamma spectroscopy that demonstrates very good agreement be- tween the two methods. However, for non-accreting banks, where -'"Pb activity approaches a minimum in the upper part of the cores, the similar, more generic relationship was determined for -i"Pb and radium --"Rajp^^g = Total -'"Pb^p^g + (where dpm/g + total activity). Comparison of ages using calculated versus measured radium values yielded insignificant differences. The total -'"Pb activities for all samples ranged from dpm/g. Subtracting a background value of dpm/g for the radium content of the inost recently de- posited sediments; the maximum excess -'"Pb signal was dpin/g. A typical plot of excess -'"Pb vs. depth from Russell Bank (Core 19C) deinonstrates that Flor- ida Bay sediment are in sufficient disequilibrium for calculating accurate geochronology (Text-fig. 3). Text- figure 3 clearly shows that a discernable difference can be observed in -'"Pb and --^Ra down to a depth of 100 cm. This diagram also shows the consistent decrease in radium with depth. The core in Whipray Basin (5G) has high '"'Pb ac- tivity at the top and. interestingly, also elevated activ- ity at the bottom (Text-fig. 4). Gamma spectrometry measurements of these cores suggest that the increased activities observed in the bottom sediments are likely the result of elevated radium and uranium activities. This phenomenon has been detected in the cores taken within the Everglades; in cores from the northern por- tion of Florida Bay: Rankin Bight (Site 7). Johnson Key
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