Abstract Introduction >Background Methods Seismic Sequences Discussion Conclusions & Acknowledgments References Tables PDF Version

From the Late Mesozoic to the Cenozoic, the Florida-Bahamas megabank has been one of the most expansive systems of carbonate platforms in the Earth's geologic history (Poag 1991). From the Middle Cretaceous to the Late Paleogene, a structural low called the Suwannee Strait or Gulf Trough (Hull 1962; Popenoe et al. 1987) separated the carbonate Florida Platform from a clastic shelf and slope at the southeastern part of modern North America, and was key to maintaining carbonate sedimentation on the platform (Applin and Applin 1965; Chen 1965; McKinney 1984). In the Middle Cretaceous a strong current began to flow through this low Suwannee Strait or Gulf Trough creating a sharp facies boundary between siliciclastics originating in the southern Appalachians to the north and the carbonate mega-platform to the south. Currents moving through the seaway from the Gulf of Mexico to the Atlantic precluded transport of siliciclastic sediment and nutrients from interrupting carbonate growth on the Florida Platform (Hine 1997). Development of a paleo-Florida current during the Paleocene to Early Eocene(?) weakened the current through the Gulf Trough (Denny et al. 1994), and in conjunction with inferred uplift of the Appalachian Mountains (Riggs 1979), contributed to infilling of this seaway. The Gulf Trough was closed by the Late Eocene (Chen 1965), allowing the dispersal of siliciclastics to the eastern part of the Florida Platform, where they mixed with carbonates during the Oligocene to Late Miocene (Scott 1988; Hammes 1992; Brewster-Wingard et al. 1997; Missimer 1997; Guertin et al. 2000; Cunningham et al. 2001a). Throughout the Late Miocene to latest Early Pliocene, deposition of carbonate sediments was negligible, and thick siliciclastic coastal-plain or slope deposits accumulated over most of the eastern side of the Florida Platform (Scott 1988; Cunningham et al. 1998; Missimer 1999; Cunningham et al. 2001a). Mixed carbonate and siliciclastic deposition prevailed throughout southern peninsular Florida during the latest Early Pliocene and Late Pliocene (Missimer 1992; Cunningham et al. 2001a), then carbonate deposition finally recovered with development of the well-known Quaternary carbonate shelf and shelf margin in southernmost peninsular Florida and the Florida Keys (Enos and Perkins 1977).

Late Miocene and Pliocene siliciclastics derived from the southeastern U.S. formed a bathymetric template for deposition of the Quaternary carbonate shelf and shelf margin (Jordan et al. 1964; Ginsburg et al. 1989; Warzeski et al. 1996). The timing and mechanism for long-distance transport of these quartzose sediments across the carbonate Florida Platform has been open to speculation since early reports of their existence by Vaughan (1910). Bishop (1956), Klein et al. (1964), and Peacock (1983) proposed that siliciclastics were transported by a N-S oriented fluvial system with deposition in a nearshore, marine-to-brackish environment (Peck et al. 1979). Winker and Howard (1977) challenged the riverine hypothesis, wondering why a major river that presumably originated in Georgia would not take a more direct route to the sea, such as those followed by the Altamaha and Apalachicola rivers today, and instead would flow for a few hundred kilometers southward along the approximate center of an active structural arch. Alt (1974), Winker and Howard (1977), Kane (1984), and Scott (1988) concluded that siliciclastics in central Florida arrived instead by longshore transport. Ginsburg et al. (1989) suggested that the siliciclastics were transported southward to near the southern end of the Florida Platform by a combination of longshore and riverine transport, with currents and waves redistributing them to form a giant spit beneath the Florida Keys. More recently, Warzeski et al. (1996) mapped a trend of coarse-grained siliciclastics along the south-central portion of the peninsula and proposed that the coarse sands were evidence for a pathway of maximum paleocurrents. They further suggested that localized transport down the pathway was either riverine or by a huge prograding spit. Cunningham et al. (1998) revised the mapping of coarse-grained siliciclastics by Warzeski et al. (1996) and demonstrated a relationship between southward transport of the coarse-grained siliciclastics and an underlying paleotopographic low. Guertin et al. (1999) suggested that sea-level fluctuations and strong regional currents were principal controls in the erosion, transport, and winnowing of the siliciclastics.