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vibracore or trench, both of which provide a limited understanding of the stratigraphy. GPR can
serve to enhance stratigraphic information and provide confidence that the dated material is in
fact part of the geomorphic feature whose age is sought. In this investigation, GPR was a
valuable tool because it was used to ensure that the samples collected for OSL dating did in fact
represent the basal ridge deposit and not the eolian or dune decorated part of the ridge in
question.
Granulometric Data from the Beach Ridge Samples
The granulometric data (mean grain size, standard deviation, kurtosis, skewness)
collected over the course of this investigation provide information about the nature and source of
the sediment making up the beach ridges on St. Vincent Island. When used in conjunction with
Tanner’s method of SELF (settling-eolian-littoral-fluvial) determination (Figure 3.8) it is
possible to make some predictions as to depositional origin of the sediment making up the island.
The mean grain sizes obtained during this study (Table 4.4) indicate that the sand
comprising the St. Vincent Island beach ridge plain is fine-grained. However, the younger sets
appear to be composed of slightly coarser grained sand than the older sets. Standard deviation is
related to the mean grain size. It refers to the spread of values about the mean and is an indicator
of sorting (Leeder, 1982). Generally, mature beaches have standard deviations that range from
0.3 to 0.5 phi (Tanner, 1995). Sands that fall within this range are considered well-sorted (Folk,
1974). All of the samples collected from the beach ridges on St. Vincent Island fall within this
range (Table 4.4).
Based on mean grain size and standard deviation, the material making up the beach
ridges on St. Vincent Island can be classified as well-sorted, mature, fine-grained sand. This has
held true over the course of the island’s history as shown in Table 4.4. However, the sand
comprising the younger sets is generally slightly better sorted and slightly coarser grained than
that found in the older sets. This implies an increase in wave energy in recent years. This
increase in wave energy was likely a direct result of sea- level rise. Alternatively, this could be a
result of increased storm frequency in recent times.
Kurtosis is a measure of the sorting in the “tails” of the grain size distribution curve and
the sorting in the central portion of the curve (Boggs, 1995). If the central portion is better sorted
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