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

the rate of erosion or deposition and can change the nature of a region or environment from
erosional to depositional.
During the Quaternary, a series of glacial-interglacial cycles brought about drastic
changes in sea level. Figure 1.4 is a benthic oxygen isotope curve showing sea-level fluctuations
throughout the Quaternary. As a result of these changes, the surface of the Florida platform has
alternated between emergent and submergent. At times during the late Cenozoic glacial stages,
dry land on the Florida plateau was restricted to a few small islands along the central Florida
ridge. At the maximum extent of the last glaciation, approximately 20,000 years B.P., sea level
was near the edge of the continental shelf, approximately 130 m below its present level. Figure
1.5 is a sea-level curve for the Gulf of Mexico that spans the past 20,000 years. During the
Quaternary sea-level cycles, river and stream systems traversed the entire continental shelf. At
about 6,000 years B.P. the rate of sea-level rise slowed. As sea-level rise slowed, modern barrier
islands, like St. Vincent Island, on the northwest coast of Florida, began to form.
Apalachicola River
The Mississippi, Rio Grande, Brazos, Sabine and Suwannee Rivers are the only major
rivers that carry sediment directly to the Gulf of Mexico (Davis, 1997). The other rivers,
including the Apalachicola River, lose their sediment load in the numerous estuaries that are
isolated from the open coast by chains of barrier islands (Davis, 1997). The Apalachicola River
starts where the Chattahoochee and Flint Rivers merge (Fernald and Purdum, 1992) (Figure 1.6).
The geology of the Florida Panhandle coast of the northeast Gulf of Mexico has been strongly
influenced by the Apalachicola River (Donoghue and Tanner, 1992). The Apalachicola River is
the largest river in Florida and 21 st largest in the contiguous United States (Donoghue and
Tanner, 1994) with a drainage basin covering an area of over 60,000 square km (McKeown et
al., 2004) and having a mean discharge of 660 m 3 /s (Raney et al., 1985). The river drains an
extensive area stretching from the Piedmont in Georgia to eastern Alabama and southward to the
Gulf Coast (Stewart and Gorsline, 1962). Its drainage basin includes the southern Appalachians,
a portion of the Piedmont and the Gulf Coastal Plain (Schnable and Goodell, 1968). Figure 1.6
shows the extent of the Apalachicola River’s drainage basin.
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