the florida state university college of arts and sciences evolution of ...

atio between the first and the fifth point fell between 0.95-1.05. All OSL data were analyzed
using the ANALYST software package created by Duller (1999).
Paleodose measurements were made on single aliquots of 9.6 mm diameter. In each case,
13-20 aliquots from each sample were analyzed. The dose rate calculation relies on the thick-
source ZnS (Ag) alpha counting technique for elemental concentration determination of uranium
and thorium. Potassium was measured by ICP90 using the sodium peroxide fusion technique.
The cosmic ray gamma contribution to the sands was estimated for each sample as a function of
depth and elevation following Prescott and Hutton (1994).
Water in the sediment absorbs part of the radiation that would otherwise reach the grains
(Aitken, 1998). The dose rate in sediment containing moisture is less than that in the same
sediment if it is dry. If the effect of moisture is ignored the age may be underestimated. Water
attenuates the radiation dose, therefore, the difference between using the higher versus the lower
paleodose value in the age calculation may affect the outcome by several hundred years.
Although moisture content can be measured when the sediment is collected and a correction
obtained, it is the average moisture content over the entire burial period that is relevant (Aitken,
1998). An estimate is made by taking into account the percent moisture as sampled, and
whatever indications are available about past variations (Aitken, 1998). The water content of the
samples is measured in the laboratory using standard methods. As there is no way of knowing
the average water content of the sediments since deposition, nor of knowing if the measured
values are fully representative of present conditions, the ages of all samples are typically
calculated using a value in the high range of water content and a value in the lower range of
water content. In the case of the present project, given the fact that regional sea-level has been
very close to present during the period in question, groundwater conditions have probably been
close to present for most of the time since deposition of the sand ridges. Therefore, for the St.
Vincent samples, the assumed mean water content estimates will likely provide the most accurate
age estimates. The methodology described above was tested by collecting and dating a sample
with a known age. This sample was collected from the modern beach surface and expected to
yield an age of 0 years.
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