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

time of deposition of sandy coastal features, such as beach ridges, represents the age of the
feature. The recent development of the single-aliquot regenerative-dose (SAR) protocol for
quartz OSL, as used in the present study, has led to an increase in the accuracy of the dating
method (e.g., Duller, 1991; Wintle, 1997; Murray and Roberts, 1998; Murray and Wintle, 2000;
VanHeteren et al., 2000; Murray and Olley, 2002; Leigh et al., 2004). OSL has been found to
be highly accurate in dating similar coastal sand features, when compared with known historical
ages (Ballarini et al., 2003). For the present study, unexposed quartz sand samples extracted
from the trench walls in beach ridges and from vibracores collected in beach ridges have been
dated at the University of Georgia Luminescence Laboratory.
Standard OSL analytical techniques were applied. Sample preparation and handling for
the OSL dating was conducted under subdued red-light conditions. Five centimeters of sediment
was removed from each end of the aluminum sample tubes for dose-rate estimation.
Luminescence measurements were made on the central section of the sediment cylinder, the part
that was least likely to have been exposed to sunlight during sampling (Figure 3.5). All samples
were treated with 10% HCl and 30% H2O2 to remove carbonate and organic matter. Samples
were then sieved to extract the 150-170 μm size fractions. Quartz and feldspar grains were
separated by density, using Na-polytungstate (ρ=2.58 g/cm 3 ). The quartz fraction was then
etched using 48% HF for 80 minutes followed by 36% HCl for 30 minutes to remove the outer
surface, which might have been affected by alpha radiation. The quartz grains were mounted on
stainless steel discs using Silkospray TM . Light stimulation of the quartz was achieved using a
Risø array of blue LEDs centred at 470 nm. Detection optics comprised two Hoya 2.5 mm thick
U340 filters and a 3 mm thick Schott GG420 filter coupled to an EMI 9635 QA photomultiplier
tube. Luminescence Measurements were taken with a Risø TL-DA-15 reader as shown in Figure
3.6. A 25-mCi 90 Sr/ 90 Y built in beta source was used for sample irradiation.
The single aliquot regenerative dose (SAR) protocol (Murray and Wintle, 2000) was used
to determine the paleodose. A five-point measurement strategy was used with three dose points
to bracket the paleodose, a fourth zero dose and a fifth repeat-paleodose point. The repeat
paleodose is measured to correct for changes in the sensitivity of the sample to the applied
radiation doses and to check that the protocol is working correctly. All measurements were made
at 125°C for 100 seconds after a pre-heat to 220°C for 60 seconds. For all aliquots, the recycling
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