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

transpo-depositional history of a sample. Not all sand masses are moved by a single transport
agent. Sand deposits delivered from one agent to another, may not lose the granulometric
fingerprint of the first until considerable time has passed (Balsillie, 1995). It is important to
recognize that there may be two or more agents responsible for transport. Since all of the St.
Vincent Island samples plot at the edge of the river field in Figure 4.34, at first glance this would
suggest that the last transport and depositional agent was riverine. However, the ridges on the
island are composed of beach sand and were not directly formed by riverine processes. The
sediment may have had a riverine source (the nearby Apalachicola River and delta whose
locations are shown in Figure 1.6) originally but it is likely that several other transpo-
depositional processes were involved before the sediment was used to construct the beach ridges
on the island, with not enough time having elapsed to erase the initial riverine signature.
Figure 4.35 is a plot of skewness versus kurtosis. In general, beach and river sands tend
to be skewed to the coarse side (skewness < 0.1). Settling tail or closed basin sediments are
skewed to the fine side (skewness > 0.1). Eolian sands also tend to show a positive skewness.
With the exception of sets B and C, the St. Vincent Island samples are beach or river sands. Set
B plots as eolian and Set C is unknown since it plots outside of the limits of the graph.
Based on Figures 4.34 and 4.35, it is evident that one of the previous transpo-depositional
mechanisms for the St. Vincent Island samples has been riverine. The sediment making up the
island was likely originally derived from the Apalachicola River mouth and underwent several
modes of transport before being incorporated into the St. Vincent Island beach ridge sets.
However, it is difficult to make firm conclusions about the depositional agents because the
number of samples collected from the ridge sets is variable (Table 4.4). Sets A, B, C and D are
represented by single samples. Sets E, F, H, I, J, K and L are represented by fewer than 10
samples. Twenty-six samples were collected from set G. With the possible exception of set G,
any predictions drawn about the transpo-depositional mechanisms of the beach ridge sets on St.
Vincent Island are tentative.
Geochronologic Data from the Beach Ridge Samples
Prior to the present study, three dates were available for the island. One is an
archaeological date of 3,000-3,500 years on midden ceramics from the northwest part of the
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