Jurassic (Tithonian) radiolaria from La Désirade (Lesser Antilles): Preliminary paleontological and tectonic implications

Jurassic (upper Tithonian) Radiolaria recovered from bedded, red ribbon cherts on La Désirade, Guadeloupe, are the oldest fossils yet discovered in the Lesser Antilles. This age not only corroborates contested isotopic ages for the igneous basement of La Désirade but also demonstrates that previously reported differences in basement ages for the central and eastern end of the island are invalid. In addition, La Désirade chert yielded a higher‐latitude, Northern Tethyan to Southern Boreal Realm radiolarian assemblage (indicating deposition at a minimum of 22° north or south of the Jurassic paleoequator). Because Northern Tethyan or Boreal Jurassic oceanic crust did not exist in the spreading gap between North and South America, or east to Eurasia, we conclude that La Désirade oceanic crust formed in the Pacific. The fact that no Upper Jurassic red ribbon chert has been found in the Atlantic Ocean or in the Caribbean aside from in displaced oceanic fragments in Puerto Rico and the Dominican Republic lends additional support to a Pacific origin for the oldest crustal fragment in the Lesser Antilles.