The San Cayetano Formation of western Cuba is the thickest and most extensive subaerial exposure of Jurassic siliciclastic rocks between the southeastern United States and northern South America. Previous workers have speculated that siliciclastic rocks of the San Cayetano Formation were derived from one of the following sources: (1) Yucatan Peninsula, (2) Florida, and (3) northern South America. To address the problem of the provenance of the San Cayetano Formation and the Mesozoic position of western Cuba, we present the results of 40Ar/39Ar isotopic dates from 67 single detrital mica grains from four samples of the San Cayetano Formation. These mica grains have ages that fall within the age ranges of well-known Precambrian crustal-age provinces and Paleozoic orogenic belts in eastern North America and the Yucatan Peninsula. The lack of grains with ages in the 700–550 Ma range suggests that Pan African–Brasiliano orogenic belts that exist in northern South America, northwestern Africa, and beneath Florida did not contribute significant amounts of detritus to the San Cayetano basin. We propose that the Late Jurassic San Cayetano basin formed as a post-rift deltaic complex along the southeastern margin of the Yucatan Peninsula and was detached and transported to its present position in western Cuba in Paleogene time by the northeastward migration of the Caribbean arc.