Regional Subsurface Stratigraphy and Structure of Florida and Southern Georgia

Abstract

Sediments from Recent to Lower Cretaceous age are known to overlie the crystalline basement rocks of Florida, and beds older than Cretaceous are probably present between the Lower Cretaceous and the crystalline rocks. The thickness of the sedimentary cover resting on the basement rocks ranges from 4,350 feet in southeastern Georgia to more than 11,600 feet at the southern end of the Florida peninsula. The present discussion of the subsurface sedimentary section begins with the Oligocene and takes up the stratigraphic units in descending sequence. The known and probable underground areal extent of each unit is shown by a paleogeographic map; and the lithologic and microfaunal characteristics and variations in thickness of each are described. Relationships between the sedim ntary and faunal facies of the clastic rocks in north and west Florida and limestones of the peninsula are discussed and correlations suggested. A tentative correlation of the Florida subsurface stratigraphic section with that of Texas is also made. Five new local names are introduced for the peninsular subsurface stratigraphic units discussed in this paper. The definitions of the stratigraphic units are graphically shown by the logs of 21 wells setting forth the important lithologic and paleontologic variations disclosed by examination of samples, and they are amplified by four cross sections through wells. Five plates of microfossils characteristic of the several stratigraphic units accompany the article. The Tertiary stratigraphic units discussed include the Oligocene Suwannee limestone and Vicksburg group; the upper Eocene Ocala limestone; the late middle Eocene Avon Park limestone, Tallahassee limestone, and equivalent non-fossiliferous facies; the early middle Eocene Lake City limestone and equivalent beds of Cook Mountain age of the clastic facies; the lower Eocene Oldsmar limestone and equivalent beds of Wilcox age of the clastic facies; the Paleocene Cedar Keys limestone and equivalent beds of Midway age of the clastic facies, including the Tamesi (Velasco) faunal unit. The upper Cretaceous units are the Lawson limestone and equivalent beds of Navarro age of the clastic facies, beds of Taylor age in both limestone and clastic facies, beds of Austin in both limestone and clastic acies, and the Tuscaloosa formation. The oldest units discussed are undifferentiated Lower Cretaceous limestone and clastic rocks of possible Trinity age. A brief discussion of the regional structure indicates five major features which are further defined by structural and isopach maps and cross sections.