During the Cretaceous varying amounts of marine and non-marine sediments were deposited in the North Andean geosyncline which passed through Venezuela, Colombia, and Ecuador. During the maximum period of flooding, all except extreme Western Colombia, part of Eastern Colombia, and a few islands appear to have been covered by the seaway. The Cretaceous sediments usually begin with a sandstone or limestone, which is followed by a thick sequence of black shales with occasional limestone members. Following the black shales, there is a more or less cherty shale or limestone, which is followed by either sands and shales or shales and limestones. The thickness of the sediments varies from around 2,000 feet to more than 40,000 feet. Marine faunas are often abundant and show marked relationships to both the Gulf Coast and the European Cretaceous faunas. From the faunas collected at various localities it appears that most, if not all of the standard Cretaceous section is represented in Colombia.

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