Abstract

The Tertiary formations of the Islands Margarita and Cubagua comprise fossiliferous sedimentary rocks of Eocene, Oligocene, Miocene, and Pliocene age. Remnant blocks of limestone with Midwayan fossils are also reported. The orbitoid-bearing Punta Carnero Formation is about 2000 m thick. The Oligocene Los Vagres limestone contains a coral fauna which is related to that of the San Luis limestone of Falcón. About 300 m of mottled graywacke in Cubagua borehole No. 1 is considered to be Oligocene and is correlated with the San Lorenzo Formation of eastern Falcón. Miocene clays and sands are about 1600 m thick in Cubagua borehole No. 2. On Cubagua and Margarita these rocks are unconformably overlain by the Cubagua Formation with fossils known from the Caujarao, La Vela and Ojo de Agua Formations of Falcón. Pliocene is represented on Cubagua by about 10 m of fossiliferous sandy marl with Lyropecten arnoldi, a marker fossil of the Cabo Blanco Formation.

The Eocene and the lower Oligocene rocks are strongly folded. The upper Oligocene Los Vagres limestone appears to rest unconformably on vertical dipping lower Eocene. In the deep structural trough of Cubagua the lower Miocene was found also to be compressed. The middle and upper Miocene was less affected by orogenic movements, of which at least two phases are recognized by unconformities at the base of the Caujarao and of the younger La Vela Formation.

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