LATE EOCENE TO PLEISTOCENE IMPACTS OF ALTERNATING NEARSHORE AND FLUVIAL TRANSPORTED SILICICLASTIC SEDIMENTS TO SOUTHERN FLORIDA

From the time of its initial formation in the Jurassic-Cretaceous, the Florida Platform was an isolated feature consisting of carbonate and evaporitic sediments with no influence of siliciclastic sediments from the southern Appalachian Mountains. Transport of siliciclastic sediment sources from the north was blocked by a deep-water feature termed the Suwannee Channel. Beginning in the Late Eocene, within the Ocala Formation in southwestern Florida, the first occurrence was found of siliciclastic sediments transported by nearshore process during low sea level stands. Siliciclastic sediment also occurs in the Early Oligocene Suwannee Limestone, where 10 m thick quartz sand units are observed as linear features. Throughout the Early and Middle Miocene, quartz sand was transported via nearshore processes to southwestern Florida and was homogenized within facies in the Arcadia Formation. A major change occurred near the end of the Late Miocene when fluvial transport of sediment became a significant factor in southern Florida. Course-grained sediment containing discoid quartz and quartzite pebbles (up to 4 cm in diameter), f-feldspar, minor amounts of plagioclase, and some fine grains of feldspathic rhyolite near the base of the channels were deposited. In the Early Pliocene, fluvial-transport of fine-grained, muddy sediments blanketed large parts of the southern part of the Florida Platform. Fluvial sediment transport to southern Florida ended in the Late Pliocene, when nearshore marine-transported quartz sand entered the platform to mix with carbonate sediment forming in place. During the Pleistocene, the quantity of marine-transported siliciclastic sediment influx reduced as evidenced in the Caloosahatchee and Fort Thompson Formations, which contains quartz sand in nearly every facies, including coralline boundstones. The composition and geometry of southern Florida sediment has been influenced greatly by the interplay of nearshore and fluvial transport mechanisms from the Late Eocene to the modern day.