The fossiliferous limestone of Maestrichtian (upper Cretaceous) age, previously thought to form part of the Guaduas formation of the Magdalena region, Colombia, is shown to be included in the topmost bed of the underlying Cimarrona formation. The age of the Guaduas formation, previously described as upper Cretaceous or in part Tertiary, is thought to be chiefly Tertiary.

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