Palaeogene

The Palaeogene is the geological period from 66.00 to 23.04 million years ago in the consulted chart. It contains the Paleocene, Eocene and Oligocene, preceding the Neogene within the Cenozoic.^[ref]

The Oligocene is a geological epoch within the Palaeogene, between the Eocene and Miocene, approximately 34 to 23 million years before the present. It is also the corresponding interval of rock strata in chronostratigraphic classification.

The boundaries are defined using reference sections and correlation criteria, while their numerical ages are calibrated by dating and can be refined. A rock is therefore not assigned to an epoch solely because a rounded age estimate falls inside a convenient numerical interval. Fossils, stratigraphic relationships and independent dating must be interpreted together.^[ref]

The Eocene is a Palaeogene epoch following the Paleocene, approximately $56$ to $33.9$ million years ago.^[ref] Its strata are used in paleoclimate reconstruction, where oxygen isotope ratios and other material properties must be calibrated against the physical conditions that produced them. The stratigraphic label identifies time, rather than one globally uniform sediment type.

The Paleocene is the earliest Palaeogene epoch, approximately $66$ to $56$ million years ago.^[ref] It follows the Cretaceous and precedes the Eocene. Correlating the same interval between separated sedimentary rocks requires independent stratigraphic evidence; thickness alone is insufficient because deposition rates, erosion and missing intervals differ between sites.