Stratigraphy of the area between Hernando and Hardee counties, Florida

Abstract

Eocene, Oligocene, Miocene, and Recent rocks are exposed between Hernando and Hardee Counties. Eocene and Oligocene formations are fossiliferous limestones but Miocene rocks are largely unconsolidated sands and clays in which fossils are scarce. Correlation of Miocene strata therefore is necessarily based mainly on lithology and stratigraphic position. Where rocks are altered by weathering, correlation is based on original rather than present gross Tithelogy. Quartz sand was found to be valuable in correlation because it is not affected by weathering. Rocks in the report area previously mapped as the upper Miocene or lower Pliocene Alachua and Bone Valley formations .were found to range from lower to middle Miocene and are assigned to the Tampa and Hawthorn formations. The Citronelle formation of Pliocene or later age apparently does not extend into peninsular Florida, Clayey sand that has been considered as Citromelle equivalent in the report area is late middle Miocene or early upper Miocene in age. Hardrock phosphate deposits in the area are in lower Miocene beds which are assigned to the Tampa Limestone. Hardrock phosphate particles appear to consist of two types: cementation concretions and limestone replacements. Land-pebble phosphate deposits range in age from middle Miocene to Pleistocene. In the area of this report they are mainly residual deposits of middle Miocene age. In the report area uranium is confined mainly to lower and middle Miocene rocks with the greatest concentrations in the Hawthorn formation.