Jagua Formation  The Jagua Formation is a Late Jurassic (middle to late Oxfordian) geologic formation in the Sierra de los Órganos and Sierra del Rosario mountain ranges in Pinar del Río Province, western Cuba. Plesiosaur, pliosaur, pterosaur, metriorhynchid, turtle and dinosaur remains are among the fossils that have been recovered from its strata. The formation comprises marine shales and limestones. The thick Jagua Vieja Member consists of black shales and horizontally laminated marly micritic to biomicritic limestones. The latter contains calcareous concretions which the fossils are found in. The formation overlies the San Cayetano Formation and is overlain by the Guasasa Formation. The bedding direction is steeply dipping towards the northwest.