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(sorting). Standard deviation decreases with distance away from the river mouth. This suggests
that sorting improves with distance away from the Apalachicola River mouth. Figure 4.39 shows
the relationship between skewness and river mouth location. Skewness is smallest at the river
mouth and increases to the east and to the west of the river mouth. Figure 4.40 shows kurtosis
versus relative location. Kurtosis appears to increase from west to east.
The suite of samples collected from site SVI 009 were also analyzed. The results of the
analyses are presented in Table 4.4. The samples collected along the bedding plane show
minimal change in mean grain size, kurtosis, skewness and standard deviation. There is also
minimal change in sediment characteristics along the transect from the top of the trench to the
base of the trench. This suggests that the bedding planes within the beach ridges on St. Vincent
Island are not readily identifiable based solely on granulometry.
Geochronologic Results
Optically stimulated luminescence (OSL) ages were derived from single samples taken
from near the bases of the beach ridges at sites SVI 002, 004, 015, 023, 024 and 025, plus three
samples dated in a vertical profile down the ridge at site SVI 003. A sample was also collected
from the modern (zero-age) beach surface at site SVI 019 to test the robustness of the dating
technique used. Table 4.6 lists the OSL ages obtained in this study. The OSL depositional ages
range from zero to approximately 4,100 years. The ridge with the oldest age is the northernmost
site and the ridge with the youngest age is the southernmost site. The three ages from the vertical
profile at side SVI 003 are statistically indistinguishable. An average of the three ages is used
for the depositional age of the ridge. Figure 4.41 is a map showing the OSL ages relative to the
beach ridge sets delineated by Stapor (1973).
Ages were calculated using both the measured moisture content and average estimated
moisture content. The importance of moisture content and the methods followed to measure
moisture content are discussed in Chapter 3. Both measured and estimated moisture contents are
shown in Table 4.6. The water content of the samples varied from 2.3 to 27.8%. However, it is
possible that water may have been lost from some shallower samples by drying of the trench
walls as a result of horizontal flow and also evaporation. Given that regional sea-level has been
very close to present or slightly above it since island sediment deposition began (Figure 1.5), and
given that 5 of the 10 samples have a water content near 20%, it is likely that water content has
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