Paleogene

The Paleogene Period is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 Ma to the beginning of the Neogene Period 23.04 Ma. It is the first period of the Cenozoic Era, the tenth period of the Phanerozoic and is divided into the Paleocene, Eocene, and Oligocene epochs. The earlier term Tertiary Period was used to define the time now covered by the Paleogene and subsequent Neogene periods; despite no longer being recognized as a formal stratigraphic term, Tertiary sometimes remains in informal use. Paleogene is often abbreviated Pg, although the United States Geological Survey uses the abbreviation Pe for the Paleogene on the Survey's geologic maps.