the second of six stages (in ascending order) subdividing Miocene (Miocene Epoch) rocks, representing all rocks deposited worldwide during the Burdigalian Age (20.4 million to 16 million years ago) of the Neogene Period (the past 23 million years). The stage is named for outcrops in the French region of Bordeaux (ancient Burdigala), particularly for the fossiliferous faluns de Bordeaux in the Aquitaine Basin of southwestern France. The formal lower boundary of the Burdigalian Stage has yet to be established; however, the upper boundary approximates the zone of the first appearance of the foraminiferan (pseudopod-using unicellular organism protected by a test or shell) Globigerinatella insueta. The Burdigalian Stage is underlain by the Aquitanian Stage and overlain by the Langhian Stage.