uppermost division of Paleocene (Paleocene Epoch) rocks, representing all rocks deposited worldwide during the Thanetian Age (58.7 million to 55.8 million years ago) of the Paleogene Period (65.5 million to 23 million years ago). The Thanetian Stage is named for the Thanet Sands, Isle of Thanet, Kent, Eng.

The lower boundary of the Thanetian Stage is coincident with the first occurrence of the calcareous nannoplankton (a single-celled, photosynthetic organism with a shell made up of calcium carbonate plates called coccoliths (coccolith)) Areoligeria gippingensis. The upper boundary (equivalent to the boundary between the Paleocene and Eocene epochs) is coincident with the first appearance of the dinoflagellate (single-celled, aquatic organisms with two dissimilar flagellae and exhibiting traits of both plants and animals) Apectodinium augustum. The Thanetian Stage overlies the Selandian Stage and precedes the Ypresian Stage.