BARTONIAN STAGE

the third of four divisions (in ascending order) of the Eocene Series, representing all those rocks deposited worldwide during the Bartonian Age (43.6 to 40 million years ago). Together with the underlying Lutetian Stage, it constitutes the Middle Eocene; the Bartonian is overlain by the Priabonian Stage. The stage's name is derived from the Barton Beds found between Highcliffe and Milford-on-Sea in Hampshire, England, which traditionally served as the stratotype section. The Barton Beds are a sequence of clays and sands that are rich in the greenish, iron-bearing mineral glauconite. The Bartonian Stage is commonly defined by the biozones of the foraminiferans Orbulinoides beckmanni and Truncorotaloides rohri.