Abstract
During the past 24 years, the Neogene geology of northwestern Lee County has been studied in numerous dewatered, shell pits. The thickness of the stratigraphic section studied is about 30 feet and contains three formations; the Tamiami, the Caloosahatchee, and the Fort Thompson. The Tamiami Formation is a predominantly siliciclastic unit, equivalent to the Sand Facies of Missimer (1992) with one occurrence of the Pinecrest Member (predominantly aragonitic mollusk shell) at Acline (Charlotte County). The Caloosahatchee Formation is a mixed carbonate and siliciclastic unit that is divided into three separate units by two intraformational unconformities. The Fort Thompson Formation is a shell and quartz sand unit that contains two or three stratigraphic units. From the base to the top of the formation, the relative percentage of quartz sand increases from about 20 to 100% by volume. The lithostratigraphy of the shallow Neogene sediments adjacent to Charlotte Harbor shows that numerous transgressive and regressive sea level events produced a series of depositional environment changes over the last 4 million years. The region was blanketed with a sheet of quartz sand similar to the West Florida Shelf of today during the Pliocene as the Tamiami Formation was deposited. During deposition of the Caloosahatchee Formation, the region was subtropical with predominantly carbonate deposition and a coastal influx of quartz sand. Tropical and subtropical mollusks and corals were abundant in the region producing an environment similar to the present area between Cape Sable and Florida Bay. Deposition of the Fort Thompson Formation brought a substantial change to the environment with an evolution to barrier island and shallow nearshore deposition patterns similar to those observed today.