PRELIMINARY GEOLOGIC MAP OF PRE-MIDDLE JURASSIC BASEMENT ROCKS BENEATH THE COASTAL PLAIN IN FLORIDA

Basement terranes and rift basins concealed beneath the Atlantic and Gulf Coastal Plain are among the last frontiers of regional geology in the United States. Use of the term “basement rock” here includes Paleozoic and older crystalline and sedimentary rocks as well as rift-related Triassic to Early Jurassic sedimentary and igneous rocks. The basement architecture of Florida consists of the Gondwanan (West African) Suwannee terrane which was accreted to Laurentia during the Alleghanian orogeny and subsequently intruded by Permian granites, superposed by Early Mesozoic rift basins, and partially overlain by bimodal Jurassic volcanic rocks. The younger basement components, specifically the southwestern Florida Mesozoic volcanic province (Jsf), North Florida tholeiites (Jt) of the Central Atlantic Magmatic Province, early Mesozoic rift basins (JTrb), and Permian granitoids (Pg), have correlative and contemporaneous units throughout the Appalachian orogen. In contrast, Florida’s older basement rocks, including Paleozoic siliciclastic strata of the Suwannee basin (D€sb), North Florida volcanic series (€Znf), Osceola and Gaskin intrusive complexes (Zo and Zg, respectively), and the St. Lucie Metamorphic Complex (Zsl), have neither surface exposures nor unequivocal correlates anywhere. Major structures include early Mesozoic normal faults and the NW-striking Florida transfer zone (Jay fault). Top-of-basement structure contours show gentle arches and embayments characteristic of overlying coastal-plain strata.

This 1:1M-scale geologic map is produced by the USGS Coastal Basement Geology of the Southeastern U.S. Project with the support of the National Cooperative Geologic Mapping Program and the cooperation of the Florida Geological Survey. Subsurface geologic mapping methodology combines petrographic, geo/thermochronological, geochemical, and mineralogical analyses of drill cores and cuttings in the context of regional geophysical data. Due to the low spatial resolution of basement penetrations, locations of map contacts are approximate but are informed by previous seismic reflection studies and newly reprocessed aeromagnetic and gravity survey data which help to constrain geologic contacts, fault boundaries, and the extents of sedimentary basins and mafic to felsic plutons.