Detrital muscovite was concentrated from a core of Lower Ordovician sandstone recovered from 1282 m in the Sun Oil Company, H. T. Parker No. 1 well, Marion County, Florida. The concentrate records a 40Ar/39Ar plateau age of 504.1±2.1 Ma. The Paleozoic sedimentary section penetrated in this well is part of an extensive subsurface Lower Ordovician-Middle Devonian sedimentary succession characterized by Gondwanan paleontological affinities. The succession has been correlated with sequences of similar age in the Bové Basin of west Africa which unconformably overlie metamorphic units of the Bassaride and Rokelide orogens in Senegal and Guinea. Muscovite within these metamorphic rocks records ca. 500–510 Ma postmetamorphic 40Ar/39Ar cooling ages and was likely a proximal source for the lower Paleozoic clastic detritus represented in the pre-Mesozoic sedimentary sequences beneath the southeastern United States coastal plain.