Abstract

The Viñales limestone fauna is correlated with the upper Portlandian on the basis of the ranges of its normally coiled ammonites and their similarity with species in the upper Portlandian of Mexico and Argentina. Genera not known below the upper Portlandian include Corongoceras, Micracanthoceras, Durangites, Lytohoplites, and Parodontoceras. Genera not known above the Portlandian include Metahaploceras, Physodoceras, and Durangites. Genera not known above the lower Tithonian include Corongoceras and Lytohoplites.

Previous correlation with the Lower Cretaceous was based mainly on identity of aptychi and similarity of uncoiled ammonites to species in the Lower Cretaceous of southern Europe. Association of these forms with normal ammonites permits no doubt as to their Portlandian age and suggests that aptychi must be used with caution in detailed stratigraphic work. Nothing in the fauna suggests the Kimmeridgian or Tithonian stages. The much younger age of the fauna than that of the Argovian-lower Kimmeridgian ammonites, described by Sanchez Roig and Marjorie O'Connell, shows that the older fossils are from the San Cayetano formation beneath the Viñales limestone, and that these formations are separated by an unconformity involving parts of the Kimmeridgian and Portlandian.

Furthermore, the study shows that undoubted Lower Cretaceous rocks have not yet been found in the West Indies, that metamorphic rocks elsewhere in the West Indies may be Jurassic, and that the regions bordering the Gulf of Mexico have a similar Jurassic history. It suggests that the Palisade disturbance is late Jurassic.

Application of these conclusions toward forming a clearer picture of events in Jurassic and Lower Cretaceous times should aid in showing the time of origin and possible distribution of mineral deposits and should be particularly useful in explorations for petroleum in the deeply buried rocks of the Gulf region.

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