Rethinking the origins of the red chert at La Désirade, French West Indies

La Desirade in the Lesser Antilles contains one of the rare fragments of Jurassic oceanic crust known on Caribbean islands. Others in the northeastern Caribbean occur on Puerto Rico and Hispaniola. These fragments each include radiolarian-bearing chert that has been linked to an origin in the Pacific Ocean. Of these, a fragment in Sierra Bermeja, Puerto Rico is clearly of Pacific origin as it contains Lower Jurassic radiolarians that predate the opening between North and South America. Red ribbon chert at El Aguacate, Dominican Republic is essentially identical to widespread radiolarites found in accreted material of the Pacific basin and from Pacific Ocean ODP Site 801. Extensive sampling in the Atlantic basin has produced no Jurassic radiolarites. Thus, based on age (the older of the Sierra Bermeja outcrops) and lithology (El Aguacate), two of these fragments are definitely of Pacific origin. Re-evaluation of the chert/pillow lava sequence on La Desirade in light of recent discoveries at spreading ridges has resulted in a revised interpretation of their probable origin. A wide range of features of these cherts indicate pelagic and hydrothermal sedimentation at an Upper Jurassic spreading ridge, one that almost assuredly existed in the eastern Pacific realm. These features include: the types of chert found on the island, lack of argillaceous partings, small outcrop size, discontinuous chert bodies, presence of limestone squeeze-ups into pillow lavas and indications of hydrothermal activity, including epidotization of basalt migrating outward from pillow margins with chert rinds that record pelagic and hydrothermal sedimentation at an Upper Jurassic spreading ridge, one that almost assuredly existed in the extreme eastern Pacific realm.