uppermost and latest division of Oligocene (Oligocene Epoch) rocks, representing all rocks deposited worldwide during the Chattian Age (28.4 million to 23 million years ago) of the Paleogene Period (65.5 million to 23 million years ago). The Chattian Stage is named for the Chatti, an ancient tribe that inhabited the Cassel region of northern Germany.

The lower boundary of the Chattian Stage coincides with the top of the zone of the calcerous nannofossil (remains of ocean-dwelling golden-brown algae) Chiloguembelina. The upper boundary is nearly coincident with the top of the zone of the foraminiferan (pseudopod-using unicellular organism protected by a test or shell) Globorotalia kugleri. The Chattian follows the Rupelian Stage of the Paleogene Period and directly precedes the Aquitanian Stage of the Neogene Period.