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

sea level. It was at this point that the ridges near site SVI 023 were formed. Sea level then
remained fairly stable with several small-scale fluctuations about its present level. The ridges in
the vicinity of site SVI 025 were formed when sea level was at its present level (800 +/- 100
years). The young ridges in the vicinity of site SVI 024 formed when sea level was slightly
lower than present (400 +/- 0 years). Since then sea level has fluctuated about present levels.
Based on the analysis of the St. Vincent Island beach ridges, it appears that beach ridges
and barrier strandplains, grow more rapidly when sea level is falling or stable. This trend was
also observed by Bristow and Pucillo (2006) on the Guichen Bay strandplain complex in
southeast South Australia. The inverse relationship between sea level rise and strandplain
progradation rate may be related to the changes in accommodation space associated with changes
in sea level. When sea level rises, water depth increases and accommodation space – the space
that is available for sediment accumulation (Boggs, 2001) – also increases. Sediment will then
accumulate offshore and is not available to the barrier island. Rising sea level may also be
associated with erosion of the ridges. When sea level is falling, accommodation space decreases
and sediment becomes available to be added to the barrier island. A falling sea level can also be
associated with increased erosion of the offshore shelf as a result of lowered wave base. This
can increase the amount of sediment supplied to the beach ridge plain. Thus, the barrier island
grows and progrades.
Based on the estimates of paleosealevel from the beach ridges (Table 4.9), with
additional data it may be possible to estimate sea level positions from beach ridges. The
assumption that paleosealevel position is represented by the elevation of the midway point
between the ridge crest and the base of the shoreface may hold true.
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