GONE OR JUST FORGOTTEN? — A RECOMMENDATION TO RECOGNIZE THE TERTIARY AS A FORMAL PERIOD/SYSTEM OF THE CENOZOIC

The term “Tertiary” was prominent on geologic time scales until it suddenly disappeared at the time of the 1989 International Geological Congress (IGC) in Washington, D.C. Later, the time scale produced for the 2004 IGC in Florence, Italy, was significantly different than previous international time scales and quite controversial: it listed the Paleogene and Neogene as the only two periods of the Cenozoic Era – the Quaternary was removed or considered informal. Subsequently, the Quaternary was restored as the youngest period of the Cenozoic and, in June 2009, the Executive Committee of the International Union of Geological Sciences formally ratified a proposal lowering the base of the Quaternary to correspond to the base of the Gelasian Stage. Although the U.S. Geological Survey (USGS) did not support the new definition of the base of the Quaternary, it adopted this change for the purpose of international consistency. Because “Tertiary” is still used by many scientists to represent the interval between the top of the Cretaceous (65.5 Ma) and the base of the Quaternary (2.588 Ma) and remains a viable term for communication in the geological sciences, we feel it is now time to reassess how the Tertiary should be defined. The terms Tertiary and Quaternary have been used on USGS geologic maps for more than a century and are still used by geologic mappers. The USGS Geologic Names Committee recommends retention of the Tertiary as a formal period/system with the Paleogene and Neogene as subperiods/subsystems. This recommendation is consistent with a 2008 proposal by Head, Gibbard, and Salvador to have the Tertiary recognized as a period/system with the Paleogene and Neogene as subperiods/subsystems. We ask for support from other geologic organizations in North America to work together to retain the Tertiary for future geoscientists.