Although sub-series/sub-epochs are not recognized as formal units by the ICS, they are tolerated in recognition of their widespread use. For completeness of information it is useful to clarify how they map on to the formal Stages/Ages. In setting this out it is important to be clear that no attempt is being made here to define these units or allocate any special status to them. The list merely reflects convention as it has developed over the years.

The informal ‘lower/early Paleocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Danian Stage/Age

The informal ‘middle Paleocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Selandian Stage/Age

The informal ‘upper/late Paleocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Thanetian Stage/Age

The informal ‘lower/early Eocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Ypresian Stage/Age

The informal ‘middle Eocene’ sub-series/sub-epoch is stratigraphically equivalent to the combined formal Lutetian and Bartonian Stage/Age

The informal ‘upper/late Eocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Priabonian Stage/Age

The informal ‘lower/early Oligocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Rupelian Stage/Age

The informal ‘upper/late Oligocene’ sub-series/sub-epoch is stratigraphically equivalent to the formal Chattian Stage/Age