MACROINVERTEBRATE PALEONTOLOGY AND CHRONOSTRATIGRAPHY OF MIOCENE-PLEISTOCENE SUCCESIONS IN THE GUAJIRA PENINSULA OF NORTHERN COLOMBIA

The Guajira Peninsula is one of the last frontiers in Colombian paleontology due to its remoteness and difficult working conditions. The desert-like environment on the peninsula provides excellent exposure of the underlying geology, which includes fossiliferous rocks that represent much of the last forty million years of northern South America’s history. Macrofossil paleontology of Cenozoic sediments on the Guajira Peninsular has been relatively ignored, despite substantial interest in the stratigraphy and tectonic features of the region, and the extensive research that has been conducted in the neighboring sedimentary basins of northern Venezuela and southern Caribbean Islands. Recent geological reconnaissance has greatly improved our understanding of the tectonics, stratigraphy, and palaeontology of this sedimentary succession.

Marine invertebrate fossils were collected from various stratigraphic units in the sedimentary succession of the Guajira Peninsula, including the Macarao (late Eocene), Siamana (late Oligocene-early Miocene), Uipta (early Miocene), Jimol (late early Miocene) and Castilletes (late Pliocene-early Pleistocene) formations. Sr-isotope dating was used to develop a detailed chronology for the Jimol and Castilletes formations, and indicate that the former unit accumulated between 17.5 and 15 Ma, while the younger unit likely accumulated between 3 and 1.5 Ma. An initial survey has been carried out on the more than 3000 specimens collected during recent fieldwork. The Jimol Formation contains nearly 200 species of molluscs, which vary in preservation from a moldic or recrystalized state through to shells that bear exquisite color patterns. The formation is most similar to the late Early Miocene Cantaure Formation of Venezuela, consistent with our Sr-isotope dating. The overlying Castilletes Formation contains a diverse fauna, although most aragonite fossils are completely dissolved (moldic). Fewer than 100 species are recorded from the unit, which is similar in composition to other late Pliocene and early Pleistocene units in northern Colombia and Venezuela. The paleoenvironments and chronostratigraphy of these units is of great significance given that they also contain a rich vertebrate fossil record.